Transvaginal ultrasonographic cervical assessment for the prediction of preterm delivery

To determine the usefulness of transvaginal ultrasonographic cervical assessment for the prediction of preterm delivery in an apparently normal population, 729 pregnant women (between 15 and 34 weeks' gestation) were randomly enrolled in the study in ten tertiary perinatal centers in Japan. Cervical parameters, including cervical length, internal os dilatation, and funneling depth, were measured by transvaginal ultrasound. The predictive values of these measurements for preterm delivery were investigated in a prospective fashion. Among various cervical parameters, cervical length showed the best correlation with pregnancy outcome. Cervical length (mm) was gradually decreased as the gestational age progressed, the regression line being y = 41.21-0.22x. When the mean cervical length minus 1 standard deviation at each gestational age was chosen as a cut-off value, the group with a shortened cervix showed a significantly high preterm delivery rate exclusively in the primigravidae (odds ratio: 4.86, 95% CI: 1.85-12.72). Internal os dilatation, in contrast, was a useful predictor in multiparous women (odds ratio: 6.00, 95% CI: 1.65-21.71). It was concluded that tranvaginal ultrasonographic cervical assessment, especially the measurement of cervical length, was effective for the prediction of preterm delivery in the primigravidae.     

Multifetal pregnancy reduction: modification of the technique and analysis of the outcome

OBJECTIVE: To modify the technique of multifetal pregnancy reduction and to study the outcome of reduced twins in comparison with nonreduced twins and high-order multiple gestations. DESIGN: Prospective controlled study. SETTING: The Egyptian IVF-ET Center, Cairo. PATIENT(S): Seventy-five patients with high-order multiple pregnancies resulting from assisted reproduction. Controls were 40 nonreduced twin pregnancies and 22 high-order multiple gestations. INTERVENTION(S): Transvaginal ultrasonically guided multifetal pregnancy reduction was performed. The first 30 cases were done using KCl as a cardiotoxic agent. The modified technique was used for the last 45 cases at an earlier gestational age (approximately 7 weeks) by eliminating the use of KCI and by aspirating the embryonic parts. MAIN OUTCOME MEASURE(S): Miscarriage rate, gestational age at delivery, birth weight, and pregnancy complications. RESULT(S): Using the modified technique, the miscarriage rate was 8.8% and 41 patients delivered between 32 and 39 weeks of gestation (mean+/-SD, 36.9+/-2.45 weeks). The mean (+/-SD) birth weight was 2,450.51+/-235.44 g. The miscarriage rate, fetal wastage rate, mean gestational age, and mean birth weight were similar in reduced and nonreduced twins and were significantly better than in nonreduced triplets and quadruplets. CONCLUSION(S): The modified technique of multifetal pregnancy reduction significantly improved outcomes, which were similar to those of nonreduced twins resulting from assisted reproduction and significantly better than those of nonreduced triplets and quadruplets.     

"Appearing twin": undercounting of multiple gestations on early first trimester sonograms

An important role of first trimester sonography is to determine whether a pregnancy is a singleton, twin, or higher order multiple gestation. We assessed how frequently sonography at 5.0-5.9 weeks undercounts multiple gestations. We identified all pregnancies at our institution since 1988 in which (1) an initial sonogram obtained at 5.0-5.9 weeks demonstrated at least a singleton intrauterine pregnancy and (2) a subsequent sonogram at 6.0 weeks or beyond demonstrated a living multiple gestation. Twenty-four (11%) of 213 dichorionic twin gestations were initially undercounted as singletons, as were six (86%) of seven monochorionic twin gestations. Among 105 higher order multiples, 17 (16%) were undercounted initially. All but one of the undercounted cases were scanned transvaginally. Undercounting occurred in both natural and assisted conceptions, and it occurred more frequently on sonograms obtained at 5.0-5.4 weeks than at 5.5-5.9 weeks (P = 0.02, Fisher's exact test). Prognosis for undercounted multiple gestations was similar to that of correctly counted ones with respect to several measures of pregnancy outcome, including the likelihood that all fetuses would be delivered liveborn, gestational age at birth, and birth weight (P > 0.20, all comparisons). In conclusion, transvaginal sonography at 5.0-5.9 weeks frequently undercounts multiple gestations. Initially undercounted multiple gestations and those correctly counted have similar pregnancy outcomes.     

Biparietal diameter: a useful measure for determining gestational age of human abortuses

BACKGROUND: The crown-rump length is conventionally used to determine the age of human abortuses. However, it is not reliable as it is dependent on the positioning of the conceptus. We compared this with the biparietal diameter and foot length for determining the gestational age. METHODS: Different measurements, commonly used to assess gestational age, were measured in 146 human abortuses for which an accurate obstetric history could not be elicited. Measurements taken were crown-rump length, biparietal diameter and foot length. These were correlated with the observations at antenatal examinations before finalizing the approximate age. RESULTS: Multiple regression analysis of the data indicated that of the three measurements, the biparietal diameter was the most reliable for determining foetal gestational age between 8 and 26 weeks. The age determined with the biparietal diameter correlated well with that of abortuses with an accurate obstetric history. CONCLUSION: The biparietal diameter of a human foetus may be used to determine its age if the obstetric history regarding the period of gestation is vague or not available.     

Management of premature rupture of membranes in a monofetal pregnancy before 28 weeks gestation

To establish appropriate management of premature rupture of the membranes before 28 weeks, we examined maternal and fetal risks in pregnancies complicated by this rare problem (1-7/1000). Three main factors were identified in such circumstances: prematurity, infection and oligohydramnios. Prematurity is inevitable and depends on three factors: gestational age at rupture of the membranes which is an independent predictor of poor prognosis before 22 weeks; gestational age at delivery as neonates born before 26 weeks gestation have an overall perinatal survival < 50%, and latency period between preterm rupture of the membranes and delivery which ranged from 1 to 161 days with a mean 7.8 days. Infection is the second factor with a high incidence (> 30%) of chorioamnionitis. The third factor is skeletal deformations and pulmonary hypoplasia predicted by severe and prolonged (> 14 days) oligohydramnios. Only about 40% of such women will take home a live baby. Successful outcome can be achieved in about 60% of these survivors. Termination of pregnancy is warranted at 22 weeks gestation or less and may be proposed. Beyond 22 weeks gestation, management is based on a wait-and-see attitude with ultrasonographic and bacteriological surveillance. After 25 weeks gestation, management becomes more active with use of antibiotics, tocolytics and steroids which can help prolong the latency period and improve fetal outcome. Ongoing counselling and psychological support are essential in the management of this morbid complication of pregnancy.     

Early transvaginal measurement of transcerebellar diameter in Down syndrome

OBJECTIVE: To evaluate the screening utility of early transvaginal measurement of the transverse cerebellar diameter for identification of Down syndrome fetuses. METHOD: Measurements of the transverse cerebellar diameter were obtained by transvaginal sonography between 11 and 16 weeks of gestation in 544 fetuses with a normal karyotype and in 37 Down syndrome fetuses. RESULTS: The transverse cerebellar diameter was found to show a fairly constant increment of values throughout the period evaluated with a linear relationship to the gestational age. The measurements obtained in Down syndrome fetuses are within the normal range for gestational age. CONCLUSION: The transverse cerebellar diameter cannot be considered a useful tool in the detection of Down syndrome in early pregnancy.     

Ultrasound evaluation of the width of the fetal nose

The aim of the study was to construct a normal range for the width of the fetal nose during gestation. The study group included 229 healthy pregnant women with normal singleton pregnancies at 15-42 weeks of gestation. The ultrasound measurements were taken at the level of the lower border of the ala nasi, using the modified coronal view. Routine biometric measurements were obtained from the participants, including biparietal diameter, head and abdominal circumferences, cerebellum and femur lengths. Our results were used to construct objective measurements of the fetal nasal width across all gestational ages. We conclude that the nasal width can be easily measured from 15 weeks of gestation using the modified coronal view. A linear growth relationship was found between nasal width and gestational age, biparietal diameter, head and abdominal circumferences, and transcerebellar and femoral lengths. We feel that such measurements may prove useful in the diagnosis of cases at high risk for fetal facial abnormalities.     

A comparative analysis of second-trimester ultrasound dating formulae in pregnancies conceived with artificial reproductive techniques

A dataset of 64 pregnancies conceived by artificial reproductive techniques was studied to assess the accuracy of second-trimester dating formulae when these were applied in routine ultrasound clinics in different centers. Dating formulae for biparietal diameter (BPD) and femur length (FL) were derived for a gestational age range of 14-23 weeks. The best fit curves represented linear equations: gestational age (days) = 44.2 + 2 x BPD; and gestational age (days) = 67.4 + 2.3 x FL. Twelve published formulae for biparietal diameter and femur length were reviewed and systematic and random errors were calculated for these formulae when they were applied to second-trimester scan measurements in precisely dated pregnancies. Overall, published dating formulae performed well in predicting gestational age. The 95% confidence interval was 8.3 days for biparietal diameter and 10.2 days for femur length. The study confirms the accuracy of ultrasound dating in routine ultrasound clinics and supports the use of ultrasound measurement alone in preference to menstrual history for dating pregnancy.     

Prenatal determination of chorionicity in triplet pregnancy by ultrasonographic examination of the ipsilon zone

OBJECTIVE: To determine chorionicity in triplet pregnancies by ultrasonographic assessment of the ipsilon zone, the junction of the three interfetal membranes. METHODS: The thickness of the component membranes in the ipsilon zone was studied to determine chorionicity in 28 triplet pregnancies, by retrospective examination of the ultrasonographic images taken at 9-24 weeks' gestation, and in 20 consecutive triplet pregnancies followed prospectively by targeted ultrasonography at 8-21 weeks' gestation. Prenatal ultrasonographic findings were compared with those obtained from the records of the infertility centers or referring hospitals (the number of gestational sacs and live embryos in each sac seen by transvaginal scanning at 6-7 weeks' gestation). RESULTS: Of the 28 triplet pregnancies with appropriate images demonstrating the ipsilon zone, 22 were classified as trichorionic, five dichorionic, and one monochorionic. This classification was correct in all but one trichorionic pregnancy, which was misclassified as dichorionic. In the prospective subset (n = 20) there were 16 trichorionic and four dichorionic triplet pregnancies. The ipsilon zone was not present in one case in which the interfetal membrane did not intersect. In the remaining 19 pregnancies, there was a complete correlation between the findings at the ipsilon zone and transvaginal ultrasonography at 6-7 weeks. CONCLUSION: Ultrasonographic assessment of the ipsilon zone is useful for predicting chorionicity in triplet pregnancies.     

Identifying hospitalized older patients at varying risk for physical performance decline: a new approach

It is not known how immaturity and disease influence postnatal thyroid function in infants <30 wk of gestational age. We performed serial measurements of plasma thyroxine (T4), free T4 (FT4), triiodothyronine (T3), reverse T3 (rT3), TSH, and T4-binding globulin (TBG) in 100 infants of <30 wk of gestation, during the first 8 postnatal weeks, to investigate the influences of disease and gestational age on the time course of thyroid hormones. One hundred infants were divided twice into two groups: 1) in a group of 25-28 and of 28-30 wk of gestation; and 2) in a sick and a healthy group, with similar gestational ages. The time course of T4, FT4, T3, TSH, and TBG, but not rT3 differed significantly (p < 0.005) between the gestational age groups. T4 and FT4 decreased to levels below the cord blood value with a deeper FT4 nadir on d 7 in the youngest group. Disease decreased T4, FT4, T3, TSH, and TBG concentrations especially during the 1st wk after birth (p < 0.005). However, the FT4 nadir on d 7 was similar in sick and healthy infants. After 3 wk, T4, FT4, T3, and TBG were higher in the sick group compared with the healthy group. rT3 levels were not increased in sick infants. We conclude that the extent of the FT4 decrease after birth in infants of <30 wk gestation is mainly influenced by gestational age and probably reflects a transient depletion of thyroidal hormone reserves. rT3 cannot be used as a marker of nonthyroidal illness in very preterm infants.     

The Diabetes in Early Pregnancy Study: beta-hydroxybutyrate levels in type 1 diabetic pregnancy compared with normal pregnancy. NICHD-Diabetes in Early Pregnancy Study Group (DIEP). National Institute of Child Health and Development

OBJECTIVE: The objective was to assess relationships between beta-hydroxybutyrate (beta-OHB) level and pregnancy outcome in human pregnancy in light of the fact that high levels of beta-OHB cause malformations and growth retardation in in vitro studies. RESEARCH DESIGN AND METHODS: We analyzed beta-OHB in prospectively collected specimens from the National Institute of Child Health and Human Development-Diabetes in Early Pregnancy Study, in gestational weeks 6-12 in diabetic (n = 204-239) and nondiabetic (n = 316-332) pregnant women. RESULTS: Levels of beta-OHB in diabetic women were 2.5-fold higher than in nondiabetic pregnant women at 6 weeks' gestation and declined to 1.6-fold above nondiabetic women by 12 weeks' gestation (P < 0.0001 at all times). beta-OHB was positively correlated with glucose levels (P < 0.0001) in diabetic mothers, probably reflecting degree of diabetic control. beta-OHB correlated inversely with glucose (P < 0.0003) (gestational week 6 only) in nondiabetic mothers, possibly reflecting caloric intake. beta-OHB tended to be lower (not higher) in diabetic and nondiabetic mothers with malformed infants or pregnancy losses, but the difference was not statistically significant. beta-OHB in diabetic mothers at 8, 10, and 12 weeks correlated inversely with birth weight (P = 0.004-0.02), even after adjusting for maternal glucose levels. beta-OHB levels were also generally lower in diabetic mothers of macrosomic infants, and week 12 ultrasound crown-rump measurements were inversely related to beta-OHB levels. CONCLUSIONS: The lst trimester beta-OHB is significantly higher in diabetic than nondiabetic pregnant women. In both groups, beta-OHB tended to be lower, not higher, in mothers who had a malformed infant or pregnancy loss. beta-OHB was inversely related to crown-rump length and birth weight. The modest beta-OHB elevation in the 1st trimester of reasonably well-controlled diabetic pregnancy is not associated with malformations, probably because beta-OHB levels causing malformations in embryo culture models are 20- to 40-fold higher. The mechanism of the beta-OHB association with impaired fetal growth is unknown.     

Antro-pyloric canal values from early prematurity to full-term gestational age: an ultrasound study

PURPOSE: To evaluate antro-pyloric canal dimensions from early prematurity to full-term gestational age. MATERIALS AND METHODS: Ninety infants with no signs of regurgitation or vomiting were studied 3-5 days after birth. Their gestational ages ranged from 26 to 41 weeks (mean 33.7 weeks) and the body weight from 670 to 4150 g (mean 2067 g). Antro-pyloric muscle thickness, canal length and canal width were measured. RESULTS: A positive correlation between gestational age, muscle thickness (R = 0.71, P < 0.001), length (R = 0.63, P < 0.001) and width (R = 0.42, P < 0.001) was found. Furthermore, a positive correlation between body weight, muscle thickness (R = 0.82, P < 0.001) length, (R = 0.67, P < 0.001) and width (R = 0.55, P < 0.001) was observed. CONCLUSIONS: This study shows that antro-pyloric canal dimensions increase with gestational age. Moreover, it provides normal values for muscle thickness, canal length and canal width from the early gestation to full term.     

Ultrasonographic characteristics of first-trimester gestations in recurrent spontaneous aborters

OBJECTIVE: To compile, for the first time, serial ultrasonographic findings during the first trimester of pregnancy in women with a history of primary recurrent spontaneous abortion so as to define the dynamics of early normal and abnormal gestations in this category of gravidas. STUDY DESIGN: Transvaginal ultrasonograms were obtained weekly from 5 to 12 weeks' gestational age in 40 women, 10 each of four groups: recurrent spontaneous aborters and primiparas (controls), with both successful and failed gestations. RESULTS: Embryonic heart motion was detected in 40-50% of successful pregnancies during the fifth week of gestation and in the balance by the sixth week, while heart motion was detected in no more than 50% of pregnancies that later failed. Of the failed pregnancies, all were evident by the eighth week of gestation, including those with previously documented viability. The gestational sac size and crown-rump length were smaller than expected in both failed groups, with the sac size difference evident as early as week 5 and the crown-rump length difference apparent by week 7. CONCLUSION: Appropriate timing of the initial ultrasonogram in recurrent aborters (i.e., 8 weeks' gestational age) can identify, by means of heart motion and gestational sac features, all pregnancies that will ultimately fail.     

The relationship of pretreatment serum hemoglobin level to the survival of epithelial ovarian carcinoma patients: a prospective review

OBJECTIVE: Our purpose was to examine the impact of gestational age and fetal growth restriction on fetal and neonatal mortality rates in the postterm pregnancy. STUDY DESIGN: All deliveries occurring in Sweden between Jan. 1, 1987, and Dec. 31, 1992, were evaluated for participation in this study. Data were derived from the National Swedish Medical Birth Registry. Pregnancies were selected for inclusion in the study on the basis of the following criteria: (1) singleton pregnancy, (2) reliable dates, (3) gestational age > or = 40 weeks, and (4) maternal age 15 to 44 years. Fetal growth restriction was defined as birth weight <2 SD below the mean for gestational age. A total of 181,524 pregnancies met the inclusion criteria and formed the study population. Fetal and neonatal mortalities at 40 weeks' gestation were used as reference levels. Logistic regression analysis was used to estimate the independent effects of gestational age and fetal growth restriction on fetal and neonatal mortality rates. RESULTS: A significant rise in the odds ratio for fetal death was detected from 41 weeks' gestation and on (odds ratios 1.5, 1.8, and 2.9 at 41, 42, and 43 weeks, respectively). Odds ratios for neonatal mortality did not demonstrate a significant gestational age dependency. Fetal growth restriction was associated with significantly higher odds ratios for both fetal and neonatal mortality rates at every gestational age examined (with odds ratios ranging from 7.1 to 10.0 for fetal death and from 3.4 to 9.4 for neonatal death). CONCLUSIONS: Postterm pregnancies have long been considered to be at high risk for adverse perinatal outcome. This study documents a small but significant increase in fetal mortality in accurately dated pregnancies that extend beyond 41 weeks of gestation. This study also demonstrates that fetal growth restriction is independently associated with increased perinatal mortality in these pregnancies.     

How accurate is fetal biometry in the assessment of fetal age?

OBJECTIVE: The purpose of the study was to assess the accuracy of fetal biometry in the midtrimester of pregnancy in the assignment of fetal age. STUDY DESIGN: A total of 152 singleton, 67 twin, and 19 triplet gestations resulting from in vitro fertilization with ultrasonographic fetal biometry from 14 to 22 weeks made up the study population. A gestational age prediction equation was derived from singletons with the use of stepwise linear regression. This equation was compared with 38 previously published equations and then applied to the twin and triplet populations. RESULTS: Head circumference was the best predictor of gestational age (random error [SD] 3.77 days). Addition of abdominal circumference and femur length to head circumference improved the accuracy of the dating equation (random error 3.35 days). Most dating formulas had systematic errors of <1 week. The systematic error was -0.32 day for averaging the singleton-based predictions for twins and -1.26 days for triplets. CONCLUSIONS: Gestational age assessment with the use of fetal biometry from 14 to 22 weeks is accurate for singleton, twin, and triplet gestations.     

Study of intrauterine growth from birthweight at Maharaj Nakhon Chiang Mai Hospital

Intrauterine growth curve and normogram for newborns at Maharaj Nakhon Chiang Mai Hospital are constructed. Birthweight at various gestational weeks of deliveries were determined within 24 hrs after birth. All 1,311 Thai pregnant women selected, fitted the criteria of inclusion deliveries at Maharaj Nakhon Chiang Mai Hospital from May 1983 to April 1991 (8 yrs). Their gestational age distribution was between 28 wks to 42 wks. Clinical status at birth was satisfactory. There were no obstetric or medical complications during pregnancy. Mean birthweight and standard deviation of newborns for each gestational age at delivery were calculated and presented in tabular and graphic form. Mean birthweight for 40 wks of gestation was 3.144 +/- 382 g. In addition, normogram of 10th, 50th, 90th percentile ranks of birthweight for each gestational age was constructed. These values may be useful as baseline data of intrauterine growth curve to evaluate fetal growth in our population.     

Premenstrual dysphoric disorder: controversies surrounding the diagnosis

OBJECTIVE: To evaluate the umbilical and uterine arterial Doppler flow velocity waveform systolic to diastolic (S/D) ratios performed at 24-30 weeks gestation for predicting fetal growth retardation (IUGR). METHODS: A prospective double blind study was conducted in 118 cases of high risk singleton pregnant women. The umbilical and uterine arterial S/D ratios were measured at 24-30 gestational weeks and the pregnancy outcomes were followed up. RESULTS: The prevalence of IUGR in our study population was 16.9%. At 24-30 weeks gestation, the S/D ratio of both umbilical artery and uterine artery in IUGR pregnant women were significantly higher than those in normal pregnant women, while the fetal biometric measurements were normal in all the 118 cases. The sensitivity, specificity and positive predictive value of umbilical arterial S/D ratio to predict IUGR were 80.0%, 83.7% and 50.0% with a Kappa index of 0.51 at 24-30 weeks gestation. With lower sensitivity, specificity, positive predictive value and Kappa index (40.0%, 84.5%, 34.8% and 0.23 respectively), the uterine arterial S/D ratio had less predictive value. CONCLUSIONS: The umbilical arterial Doppler flow velocity waveform S/D ratio may be an earlier predictor for screening of IUGR at 24-30 weeks gestation in high risk pregnant women with normal fetal biometric measurements.     

Does advanced maternal age affect pregnancy outcome in women with mild hypertension remote from term?

OBJECTIVES: Our purpose was to compare maternal and perinatal outcomes of mature women with those in younger women with pregnancies complicated by mild hypertension remote from term. STUDY DESIGN: A matched cohort design was used. A total of 379 mature pregnant women (> or = 35 years old) with mild hypertension remote from term were matched for race, gestational age, and proteinuria status at enrollment with 379 adult controls aged 20 to 30 years also with mild hypertension remote from term. All were enrolled in an outpatient management program that included automated blood pressure measurements and daily assessment of weight, proteinuria, and fetal movement. RESULTS: The mean gestational age at enrollment was 32.7 +/- 3.0 weeks for both groups (range 24 to 36 weeks). By matching 20.6% of patients in each group had > or = 1+ proteinuria on urinary dipstick at enrollment, and 77.3% of patients in each group were white. Chronic hypertension was more common in the mature group (22.4% vs 14.5%, p = 0.007). The mean gestational age at delivery (37.2 +/- 2.3 vs 37.2 +/- 2.2 weeks), the mean pregnancy prolongation (28.1 +/- 21.0 vs 28.4 +/- 22.0 days), and the mean birth weights (2864 +/- 770 vs 2906 +/- 788 gm) were similar between the mature and younger groups (all p > 0.05). There were no differences regarding abruptio placentae (2 vs 3 cases) or thrombocytopenia or HELLP (hemolysis, elevated liver enzymes, low platelets) syndrome (7 vs 9 cases), and there were no cases of eclampsia. There were five stillbirths in the mature group and none in the younger group (p = 0.063). CONCLUSION: Outpatient management of mild hypertension remote from term in the mature pregnant women was associated with similar maternal outcomes but with a nonstatistically higher stillbirth rate compared with the younger pregnant woman.     

Sonographic evaluation of fetal growth: growth rate variability as a function of the interval between examinations

OBJECTIVE: Fetal growth rates determined on the basis of findings at two separate sonographic examinations can be used to detect growth abnormalities. This article determines the relationship between the length of the interval between examinations and the associated variability in measured fetal growth rates. MATERIALS AND METHODS: We analyzed 1479 fetal measurements of the biparietal diameter, average abdominal diameter, and femur length from 539 normal pregnancies. Mean growth rates were computed as functions of gestational age. The standard deviation of the growth rate was computed as a function of the interval between examinations. RESULTS: The standard deviation of fetal growth rates is relatively constant when the interval between examinations is 8-10 weeks or more, but increases substantially when the interval is fewer than 6 weeks. CONCLUSION: From a purely statistical point of view, the optimal interval for assessment of fetal growth rates is 8-10 weeks or more. Shorter intervals, however, usually are mandated by the clinical situation. Correction factors can be used to determine the standard deviations and associated confidence intervals for fetal growth measured over a period of fewer than 10 weeks.     

Supplemental oxygen and gastric pH in unfed preterm infants

Hypoxia has been associated with decreased gastric acidity in infants and children. In neonates, an inverse relationship between gestational age and gastric acidity may confound this association. To assess the relationship between oxygen supplementation and gastric acidity in premature neonates, mean 24-hour continuous measurements of gastric pH, obtained by an indwelling flexible gastric pH probe, were compared in infants requiring and not requiring oxygen. Patients were < 36 weeks' gestational age and were unfed before and during the assessment period. The gestational age of infants who required oxygen was less than that of infants who did not (30.5 +/- 3.0 vs 32.9 +/- 1.5 weeks, respectively). Other comparison variables were not different. The mean pH for infants requiring oxygen (4.4 +/- 1.7) was significantly greater than that of those not needing oxygen (2.7 +/- 1.2). After controlling for population characteristics and gestational age, we found that infants requiring oxygen still had significantly reduced gastric acidity.