Gestational age and fetal biophysical assessment

Duration of biophysical profile in periviable and very preterm low-risk pregnancies

BACKGROUND

In recent years, perinatal viability has shifted from 24 to 22 weeks of gestation at many institutions after improvements in survival in neonates delivered at the limit of viability. Monitoring these fetuses is essential because antenatal interventions with resuscitation efforts are available for patients at risk of delivery at the limit of viability. However, fetal monitoring using biophysical profiles has not been extensively studied in very preterm pregnancies, particularly in the periviable period (20 weeks 0 days to 23 weeks 6 days).

OBJECTIVE

This study aimed to (1) investigate whether the completion of biophysical profiles within 30 minutes is feasible in very preterm pregnancies, and (2) determine the average observation time required to achieve a score of 8 out of 8 in very preterm pregnancies from 20 weeks 0 days to 31 weeks 6 days.

STUDY DESIGN

This study prospectively evaluated biophysical scores in singleton pregnancies undergoing routine ultrasonography at or near viability from 20 weeks 0 days to 23 weeks 6 days (periviable or group I), 24 weeks 0 days to 27 weeks 6 days (group II), and 28 weeks 0 days to 31 weeks 6 days (group III). The results and duration of biophysical profiles were compared with those of a control group (32 weeks 0 days to 35 weeks 6 days) undergoing indicated fetal surveillance. Biophysical profiles were performed for all studied pregnancies until a score of 8 out of 8 was obtained. When >1 biophysical profile was obtained during pregnancy, each was analyzed individually. Pregnancies with fetal anomalies or obstetrical/medical indications for fetal well-being surveillance were excluded. Analysis of variance and post hoc Tukey tests were used for comparisons.

RESULTS

Data were collected for 123 participants, yielding 79, 75, and 72 studies for groups I, II, and III, respectively. The control group included 42 patients, yielding 140 studies. At 30 minutes, 80% (63/79) of the studies in the periviable group had a score of 8 out of 8, as opposed to 100% (140/140) in the control group (P<.001). The mean±standard deviation time in minutes to achieve a biophysical score of 8 out of 8 was 23.3±10.1 in the periviable group, as opposed to 9.4±6.5 in controls (P<.001). Extending the study to +2 standard deviations (43.6 minutes) in the periviable group resulted in 97% (77/79) of the scans scoring 8 out of 8 in the absence of adverse outcomes. In the other groups, a biophysical score of 8 out of 8 within 30 minutes was obtained in 97% (73/75) and 100% (72/72) in groups II and III, respectively; the mean±standard deviation times were 17.1±8.4 minutes (group II) and 13.1±7.3 minutes (group III). No adverse outcomes developed during the study participation in groups I to III.

CONCLUSION

Biophysical scores of 8 out of 8 can be successfully achieved in low-risk periviable pregnancies (20 weeks 0 days to 23 weeks 6 days) within an observation time longer than the standard 30-minute duration. The time required to reach a score of 8 out of 8 decreases as gestation progresses. We suggest adjusting the observation time for biophysical profile completion according to the gestational age.

Amniotic fluid index measurements in the second and third trimester and correlation to fetal biometric parameters - new reference based on a big retrospective data

INTRODUCTION

Estimation of amniotic fluid volume (AFV) is part of routine obstetric sonography which reflects maternal-fetal circulation efficiency, fetal hemodynamic status, and a parameter for predicting adverse neonatal outcome. Fetal weight is positively correlated with AFV. Therefore, our objective is to provide a new nomogram of AFV indices and to evaluate the relation between AFV and fetal biometric parameters.

MATERIALS AND METHODS

Retrospective cohort study between 2011 and 2018, at a large tertiary medical center. Data were collected from medical charts of prenatal sonographic evaluation of normal pregnancies, including routine estimation of AFV by using amniotic fluid index (AFI). Generalized estimating equations model was used to study the association between AFI, gestational age and fetal biometric parameters. Centiles were calculated using the Generalized Additive Models for Location, Scale, and Shape model. Box-Cox-t distribution and smoothing splines were used.

RESULTS

Analysis included 28,650 pregnancies. From 25 to 41 weeks gestation, the median and fifth percentile AFI gradually decreased from 174 (IQR 157-193) to 138 mm (IQR 107-173) and from 125 to 68 mm, respectively. The change in the 95th percentile was less significant, ranging around 230 mm throughout pregnancy. Multivariate regression analysis demonstrated a significant correlation between AFI and maternal body mass index (B = -0.147; CI = -0.27 to -0.02), gestational age (B = -11.8; CI = -12.5 to -11.4), estimated fetal weight (EFW) (B = 0.05; CI = 0.049-0.053) and abdominal circumference (AC) (B = 0.94; CI = 0.95-1). There was no correlation between AFI and other fetal biometric parameters.

CONCLUSIONS

We suggest new AFI indices of singleton pregnancies. We found a positive correlation between AFI and EFW and AC.

Preterm nonstress testing: 10-beat compared with 15-beat criteria

OBJECTIVE

To evaluate the relation of different acceleration criteria to perinatal outcome for interpretation of nonstress test (NST) at 32 weeks of gestation or earlier.

METHODS

Nonstress tests within 1 week of delivery for women at 32 weeks of gestation or earlier were classified as reactive by 10-beat criteria, reactive by 15-beat criteria, or nonreactive. In women with three NSTs within 1 week of delivery, patterns were categorized into decreasing, increasing, irregular, or consistent reactivity. Perinatal outcomes included perinatal death, intensive delivery room resuscitation, 5-minute Apgar score less than 7, mechanical ventilation, necrotizing enterocolitis, intraventricular hemorrhage, and hypotension. Analysis included χ and logistic regression.

RESULTS

Seven hundred fifty-one NSTs from 488 women were assessed. Of the final NSTs before delivery, 105 (21.5%) were nonreactive, 151 (30.9%) were reactive by 10-beat criteria, 232 (47.5%) were reactive by 15-beat criteria, and 274 (56.1%) had decelerations. Unadjusted data consistently associated degree of reactivity with outcome and also associated gestational age with degree of reactivity. After adjustment for gestational age and birth weight, there was no association between NST criterion (or decelerations) and outcomes except between nonreactivity and perinatal death (odds ratio 6.1, 95% confidence interval 2.3-16.5). For 97 women who underwent three tests, all patterns were common (range 16.5-37.1%) and none was significantly associated with any outcome.

CONCLUSION

In preterm pregnancies, the criterion used for NST interpretation is much less important than the gestational age at delivery. There was no appreciable difference between the 10-beat criteria and 15-beat criteria in predicting outcome. When tested repeatedly, fetuses frequently had varying degrees of reactivity without relation to outcome.

The uses and limitations of the fetal biophysical profile

In the second half of the twentieth century, true antepartum fetal assessment became possible, mainly due to the advent of real-time ultrasound. Initially, the most widely used form of antepartum fetal assessment was electronic fetal heart rate monitoring, through the nonstress test or the oxytocin-induced contraction stress test. It was soon realized, however, that these forms of monitoring had significant limitations. The biophysical profile allows a more thorough evaluation of fetal well-being and has the potential to significantly reduce the false-positive rate of the nonstress test/contraction stress test.

[Physiology of intrauterine fetal activity]

Development of heart motions and fetal body movements are detectable by ultrasound in early gestation period. There is no identifiable triggering mechanism, thus these motions are attributed to an intrinsic autonomic mechanism. These spontaneous motions controlled by endogenous mechanisms of central nervous system represent neural functions. Most--if not all--intrauterine movements are brought about by endogenous factors through intrinsic motivation. Early intrauterine movements usually involve the whole body musculature. Initially, these are arrhythmic in nature and occur sporadically. Independent movements of extremities can be observed between the 9th and 12th gestational weeks. Frequency of movements increases between 24th and 28th weeks, then decreases between 30th and 39th weeks of gestation. External stimuli such as touch, pressure, sound or temperature change can stimulate reactive body movements. The development, organization and co-ordination of body movements are studied by ethologists, while the frequency of movements is the subject of interest of obstetricians. Although these investigations have different aims, researches often overlap in the absence of clearly identifiable borderlines. As obstetricians are rather interested in the second half of the pregnancy, 80% of relevant publications refer to this period of pregnancy.

Biophysical profile for fetal assessment in high risk pregnancies

BACKGROUND

A biophysical profile (BPP) includes ultrasound monitoring of fetal movements, fetal tone and fetal breathing, ultrasound assessment of liquor volume with or without assessment of the fetal heart rate. The BPP is performed in an effort to identify babies that may be at risk of poor pregnancy outcome, so that additional assessments of wellbeing may be performed, or labour may be induced or a caesarean section performed to expedite birth.

OBJECTIVES

To assess the effects of the BPP when compared with conventional monitoring (CTG only or MBPP) on pregnancy outcome in high-risk pregnancies.

SEARCH STRATEGY

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (October 2007), CENTRAL (The Cochrane Library 2006, Issue 4), MEDLINE (1966 to November 2006), EMBASE (1974 to November 2006) and CINAHL (1980 to November 2006).

SELECTION CRITERIA

Randomised and quasi-randomised controlled trials involving a comparison of fetal BPP with other forms of antepartum fetal assessment in women with high-risk pregnancies.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed eligibility, quality and extracted data.

MAIN RESULTS

We included five trials, involving 2974 women. Most trials were not of high quality. Although the overall incidence of adverse outcomes was low, available evidence from randomised controlled trials does not support the use of BPP as a test of fetal wellbeing in high-risk pregnancies. We found no significant differences between the groups in perinatal deaths (relative risk (RR) 1.33, 95% confidence interval (CI) 0.60 to 2.98) or in Apgar score less than seven at five minutes (RR 1.27, 95% CI 0.85 to 1.92). Combined data from the two high-quality trials suggest an increased risk of caesarean section in the BPP group RR 1.60, 95% CI 1.05 to 2.44, n = 280, interaction test P = 0.03. However, the number of participating women was relatively small (n = 280). Therefore, additional evidence is required in order to be definitive regarding the efficacy of this test in high-risk pregnancies. Furthermore, the impact of the BPP on other interventions, length of hospitalisation, serious short-term and long-term neonatal morbidity and parental satisfaction requires further evaluation.

AUTHORS' CONCLUSIONS

At present, there is insufficient evidence from randomised trials to support the use of BPP as a test of fetal wellbeing in high-risk pregnancies.

Acute respiratory distress syndrome in pregnancy

OBJECTIVE

To summarize the pathophysiology and treatment of acute lung injury and acute respiratory distress syndrome (ARDS) during pregnancy.

DATA SOURCE

Review of select articles from MEDLINE, including published abstracts, case reports, observational studies, controlled trials, review articles, and institutional experience.

DATA SUMMARY

ARDS occurs in pregnancy and may have unique causes. Despite extensive clinical research to improve the management of ARDS, mortality remains high, and few strategies have shown a mortality benefit. Furthermore, in most published studies, pregnancy is an exclusionary criterion, and thus, few treatments have been adequately evaluated in obstetric populations. The treatment of ARDS in pregnancy is extrapolated from studies performed in the general ARDS patient population, with consideration given to the normal physiologic changes of pregnancy. In general, the best support of the fetus is support of the mother. From the age of viability (24-26 wks at most institutions) until full term, decisions regarding delivery should be made based primarily on the standard obstetric indications.

CONCLUSIONS

Little evidence exists regarding the management of ARDS specifically in pregnancy, and thus, treatment approaches must be drawn from studies performed in a general patient population. A multidisciplinary approach involving maternal-fetal medicine, neonatology, anesthesiology, and intensivist clinicians is essential to optimizing maternal and fetal outcomes.

Effect of intravenous magnesium sulfate on the biophysical profile of the healthy preterm fetus

OBJECTIVE

The null hypothesis is that intravenous magnesium sulfate does not affect the biophysical profile of the healthy preterm fetus.

STUDY DESIGN

Thirty-one fetuses of 25 patients between the gestational ages of 24 and 35 weeks, median 31.4 and mean (+/- SD) 30.4 (+/- 2.9), who required tocolysis for uterine contractions were prospectively studied. After normal fetal biophysical assessment was documented, intravenous magnesium sulfate was started as a 4 or 6 gm loading dose and then infused at 2 to 3.5 gm/hr to achieve tocolysis. Blood was drawn for measurement of maternal serum magnesium levels immediately before intravenous magnesium sulfate was administered and at 2 and 12 hours after the loading dose. Biophysical profiles, consisting of a possible 12 points, were performed at the same time as blood was drawn. Serum magnesium levels were compared with one-way analysis of variance for repeated measures and biophysical profile scores with Friedman's test. Statistical significance was considered p < 0.05.

RESULTS

Mean (+/- SD) serum magnesium levels were 1.7 (+/- 0.1) mg/dl before infusion, 4.3 (+/- 0.6) mg/dl at 2 hours, and 5.2 (+/- 0.7) mg/dl at 12 hours (p < 0.001). Six fetuses did not have a 12-hour biophysical profile; three were delivered for severe variable decelerations, two progressed in labor, and in one tocolysis was discontinued. The median biophysical profile score was 11 before intravenous magnesium sulfate, at 2 hours, and at 12 hours after the loading dose. The biophysical parameters present and the percentage of fetuses with each parameter were as follows: breathing (> 30 seconds), 88% (22/25) before magnesium sulfate, 84% (21/25) at 2 hours, and 92% (23/25) at 12 hours; nonstress test (reactive), 84% (21/25) before magnesium sulfate, 68% (17/25) at 2 hours, and 80% (20/25) at 12 hours; movement (normal), 100% (25/25) before magnesium sulfate, 100% (25/25) at 2 hours, and 96% (24/25) at 12 hours.

CONCLUSION

Intravenous magnesium sulfate did not significantly alter the biophysical profile in the 25 fetuses evaluated by three biophysical profiles in spite of the significant increase in maternal serum magnesium levels.

The association between fetal body movements, eye movements and heart rate patterns in pregnancies between 25 and 30 weeks of gestation

Fetal eye movements, fetal body movements and fetal heart rate patterns were studied in healthy fetuses between 25 and 30 weeks of gestation in 21 recordings with a mean recording time of 83.5 min. In contrast with the older fetus, prolonged periods of absence as well as presence of fetal eye or body movements were uncommon. Especially absence of body movements for more than 15 min is extremely rare at this age. These findings emphasize that for the interpretation of fetal biophysical tests, gestational age should be taken into account. A linkage was demonstrated between fetal eye movements and fetal heart rate pattern and between fetal body movements and fetal heart rate pattern, but not between fetal eye movements and fetal body movements. The existence of fetal behavioural states could not be demonstrated.

The effect of magnesium sulfate tocolysis on the fetal biophysical profile

The biophysical profile has proved to be a valuable tool for the assessment of fetal well-being, independent of gestational age. Magnesium sulfate is commonly used as a tocolytic agent, yet relatively little is known about its effects on the biophysical activities of the fetus. To investigate the effects of magnesium sulfate on the biophysical profile, we performed serial studies on patients who received tocolytic therapy with this agent because of preterm labor. A total of 16 women with 22 fetuses at 26 to 34 weeks' gestation in spontaneous preterm labor were studied. An initial biophysical profile was performed at the time of admission, and a second examination was performed when maternal serum magnesium levels reached 6 to 8 mg/dl. On admission all fetuses had reactive nonstress test results and 21 of 22 (95%) demonstrated sustained fetal breathing movements. With magnesium sulfate tocolysis, 50% of fetuses had nonreactive nonstress test results, and only 4 of 22 (18%) demonstrated sustained fetal breathing movements. Fetal tone, gross body movements, and amniotic fluid volume were found to be unaffected by magnesium sulfate tocolysis.