Thomas L. Gross

Shoulder dystocia: a fetal-physician risk

Trauma that occurs as a result of shoulder dystocia is an important cause of neonatal morbidity. If the occurrence of severe shoulder dystocia, resulting in fetal asphyxia and trauma, could be accurately predicted from maternal risk factors, then a cesarean section would be indicated to prevent the poor outcome. The information available in the obstetric literature, however, is contradictory regarding whether shoulder dystocia can be predicted. In the present study, the patients at greatest risk of shoulder dystocia (all 394 mothers delivering neonates with birth weights greater than or equal to 4000 gm over a 2-year period) were examined. A three-way discriminant analysis was used to determine if a model could be developed that could effectively predict those patients who would be included in each of the groups of no shoulder dystocia, shoulder dystocia without trauma (29 patients), and shoulder dystocia with trauma (20 patients). Three factors, including birth weight, prolonged deceleration phase, and length of second stage labor, were found individually to contribute significantly to the classification. However, when examined in detail, it was noted that while 94% of cases with no shoulder dystocia would be detected, only 16% of the cases of shoulder dystocia with trauma would be predicted by this model. We conclude that in the group of pregnancies delivering neonates greater than or equal to 4000 gm, the occurrence of shoulder dystocia cannot be predicted from clinical characteristics or labor abnormalities, and that the occurrence of shoulder dystocia is not evidence of medical malpractice.

The clinical utility of maternal body mass index in pregnancy

To describe maternal body mass index and to compare the use of maternal weight and body mass index for risk assessment at the initial prenatal visit, 6270 gravid women who were consecutively delivered of infants were studied. Body mass index increased with advancing maternal age, parity, and advancing gestational age and was significantly greater in black women than in nonblack women. Risks for the development of adverse outcome associated with maternal obesity, including development of gestational diabetes, preeclampsia, fetal macrosomia, and shoulder dystocia, were comparably predicted by either maternal weight or body mass index greater than 90th percentile. Maternal weight was as predictive of preeclampsia, macrosomia, and shoulder dystocia as was body mass index when these factors were analyzed as continuous variables, whereas increasing body mass index was more predictive of gestational diabetes. The prediction of factors associated with low maternal weights, small-for-gestational-age birth, prematurity, low birth weight, and perinatal death was equivalent for maternal weight and body mass index that was less than 10th percentile. This study indicates that in the initial risk assessment of outcomes related to maternal weight, the calculation of maternal body mass index offers no advantage over simply weighing the patient. This finding contrasts with results in nonpregnant women.

Transient tachypnea of the newborn: The relationship to preterm delivery and significant neonatal morbidity☆☆☆

Early studies suggest that transient tachypnea of the newborn is a benign disease of uncertain etiology. Consequently, prevention of this complication has not been a primary concern of obstetricians. In this study of amniotic fluid phospholipids, 55 pregnancies in which the neonate developed transient tachypnea were compared to 355 pregnancies after which respiratory distress did not occur. Thirteen neonatal complications and procedures, often associated with prematurity, were significantly increased in the infants who developed transient tachypnea. Potential risk factors for transient tachypnea were examined by stepwise discriminant analysis. Negative amniotic fluid phosphatidylglycerol, prematurity (less than 38 weeks), and 1-minute Apgar score less than 7 all made an independent contribution to the overall characterization of infants at increased risk for transient tachypnea. These findings suggest that mild fetal lung immaturity may be a factor in the pathophysiology of this syndrome, and that the relationship of perinatal factors associated with transient tachypnea of the newborn in previous studies, including maternal diabetes mellitus and cesarean birth, may be partially mediated through a neonatal surfactant deficiency.

The Use of a Selected Ion Monitoring Technique to Study the Disposition of Bupivacaine in Mother, Fetus, and Neonate Following Epidural Anesthesia for Cesarean Section

&NA; It is well known that the concentration of bupivacaine in umbilical cord blood at birth is low compared with the concentration in maternal blood. It is not clear whether this low fetal/maternal ratio (F/M) is due to decreased placental transfer or increased uptake by fetal tissues. The purposes of this study were to develop an appropriate analytic method and to clarify this issue by studying the disposition of bupivacaine in mother, fetus and neonate following epidural anesthesia. The study population included 14 parturients who were delivered by Cesarean section, and their infants. Gas chromatography‐mass spectrometry techniques were developed which could simultaneously determine bupivacaine and its metabolite 2,6‐pipecolylxylidine (PPX) in maternal, fetal and neonatal body fluids to <4 ng/ml. The results indicate several points: First, that bupivacaine and PPX remain detectable in neonatal blood for at least three days. Second, that plasma levels of PPX decrease more slowly in mother and neonate than bupivacaine. Also, both mother and neonate excrete primarily PPX in urine, but a higher percentage of unchanged bupivacaine is excreted by the neonate. Finally, urinary excretion of PPX by the neonate remains relatively constant during the first 48 h of life. In contrast, the mother excretes the highest amount of PPX between 12‐24 h postpartum. The persistence of bupivacaine and PPX in neonatal body fluids suggests that the low F/M ratio of bupivacaine at birth is due to considerable uptake of bupivacaine by fetal tissues and is not due to diminished placental transfer.

Amniotic fluid phosphatidylglycerol: a potentially useful predictor of intrauterine growth retardation.

Intrauterine growth retardation, a major complication of pregnancy, remains difficult to detect reliability prior to birth. In this retrospective study of 82 pregnancies which resulted in birth of small infants, preceding clinical factors and amniotic fluid (AF) maturity tests were examined for their ability to differentiate small for gestational age (SGA) from appropriate for gestational age (AGA) infants of comparable weight. AF maturity tests included phosphatidylglycerol (PG), phosphatidylinositol (PI), lecithin to sphingomyelin ratio (L/S), PG/PI, PG/S, PI/S, foam tests, and fat cell count. Discriminant analysis revealed that AF PG was potentially the most useful parameter for predicting the birth of an SGA infant. The predictive value of PG was related to the strong correlation of AF PG with term gestation. High AF PG could potentially predict SGA infants with a true positive rate of 60%; 64% of all SGA infants could be correctly identified by means of only AF PG. The results of this study suggest that, in selected high-risk pregnancies, amniocentesis late in gestation with determination of PG may be helpful in classifying small infants as either growth retarded or preterm.

Plasma Levels of 2-Chloroprocaine in Obstetric Patients and Their Neonates after Epidural Anesthesia

The purpose of this study was to determine maternal and fetal plasma levels of 2-chloroprocaine following epidural anesthesia during labor, and to examine its metabolism by plasma cholinesterase to 2-chloroaminobenzoic acid (CABA). The study population included 33 normal patients whose infants were delivered vaginally or by repeat cesarean section, and their infants. Gas chromatographic techniques were used to determine concentrations of 2-chloroprocaine and CABA in plasma; spectrophotometric techniques were used to determine plasma cholinesterase activity. In maternal plasma 2-chloroprocaine was detectable for at least 5–10 min after each dose; mean levels at delivery were 23 ± 80 and 51 ± 13 ng/ml for patients having cesarean section and vaginal delivery, respectively. In contrast, CABA was detectable throughout labor. In cord blood plasma, 2-chloroprocaine was detectable in half of the cord-vein and arterial samples analyzed; the highest mean concentration was 17 ng/ml in samples from vaginally delivered infants. CABA was detectable in three quarters of the cord blood samples. Plasma cholinesterase activity was found to be low in both mothers and neonates, and further decreased following anesthesia in both groups. In maternal plasma, cholinesterase activity was 42 per cent less per ml plasma compared with that for nonpregnant controls, and 80 per cent less following anesthesia compared with that measured prior to anesthesia. In cord blood plasma, cholinesterase activity was 22 per cent less than that found in samples from nonpregnant women and 70 per cent less in infants whose mothers received 2-chloroprocaine than in control infants. These data suggest that the decreased activities of maternal and neonatal cholinesterases at term are adequate to hydrolyze most, but not all, of the plasma 2-chloroprocaine following epidural anesthesia during labor.

What affects fetal pulmonary maturation during diabetic pregnancy

Previous studies differ as to whether the fetus of the woman with diabetes mellitus has altered formation of lung surfactant. The factors responsible for these differences remain unclear. In this study, measures of blood glucose control, including birth weight percentile and the presence of factors potentially influencing fetal pulmonary maturation, such as diabetic class, maternal chronic hypertension, and preeclampsia, were compared with the amniotic fluid lecithin/sphingomyelin ratio, phosphatidylglycerol, and phosphatidylinositol within a group of 90 diabetic pregnancies. The factors were evaluated in combination with the techniques of canonical correlation and multiple regression analysis. Gestational age had the strongest effect in determining levels of amniotic fluid phospholipids, and hypertension was found to significantly accelerate the appearance of phosphatidylgycerol (p less than 0.05). The effect of hypertension was one third as important as that of gestational age. Neither diabetic blood glucose control, White classification, nor the remaining explanatory variables were found to play a significant role in determining the amniotic fluid phospholipid levels. This study suggests that, in the clinical management of diabetes, gestational duration remains the single most important determinant of amniotic fluid phospholipid levels.

Recurrent small for gestational age birth: Perinatal risks and outcomes

The risk of recurrent small for gestational age birth, as well as maternal and fetal-neonatal characteristics associated with recurrence, was examined in 174 mothers of consecutively delivered small for gestational age infants followed through an additional 240 livebirths. There was a twofold and fourfold increase in the risk for small for gestational age birth after one and two small for gestational age births, respectively. Although an intervening average for gestational age birth decreased the risk of recurrence, these women remained at increased risk over the general population. Given the history of a previous small for gestational age birth, perinatal risks and outcomes considered individually would not improve the prediction of recurrence. However, the significantly higher frequency of these variables, considered as a group, among mothers with recurrent small for gestational age birth suggests an association with underlying maternal disease, for example, chronic hypertension, substance use and abuse, more severe fetal-neonatal compromise, and recurrent small for gestational age birth. Recurrent small for gestational age birth should initiate a search for persistent, underlying maternal disease.

The relationship of placental grade, fetal lung maturity, and neonatal outcome in normal and complicated pregnancies

Ultrasonically diagnosed maturity changes in the placenta, Grades 0 to III, have been previously shown to correlate with fetal lung maturity. In a prospective study of 230 term and preterm complicated pregnancies, we compared the relationship between sonographic placental grading, amniotic fluid phospholipids, and neonatal outcome. The frequencies of gestational age less than 38 weeks, lecithin/sphingomyelin (L/S) ratio less than 2.0, negative phosphatidylglycerol, and neonatal hyaline membrane disease were found to decrease as placental grade advanced from 0 to III. Patients were divided into subgroups on the basis of maternal complications. In patients with Grade III placentas, the frequencies of gestational age less than 38 weeks and L/S ratio less than 2.0 were significantly increased when the subgroup of patients with chronic hypertension was compared individually to both of the subgroups, repeat cesarean section deliveries, and Classes A, B, and C diabetes mellitus (both with p less than 0.05) All three infants who developed hyaline membrane disease in association with Grade III placentas were from pregnancies of less than 38 weeks complicated by chronic hypertension. These findings suggest that the presence of a Grade III placenta is affected by both gestational age and pregnancy complications. Hence, when an elective cesarean section delivery is being planned near term gestation, a Grade III placenta is a reliable predictor of lung maturity. In preterm complicated pregnancies, an ultrasound-diagnosed Grade III placenta may still be associated with hyaline membrane disease.

Determinants of Morbidity in Obese Women Delivered by Cesarean

Studies examining the increased surgical morbidity among obese gravidas have focused mainly on differences in outcome between obese and nonobese mothers. Little is known, however, about the cause for worsened operative outcome in obese mothers or the potential impact of perioperative interventions. To define more precisely the clinical determinants of postoperative morbidity, multivariate analysis was used to relate antepartum and intrapartum variables to three measures of morbidity in 107 consecutively delivered obese women undergoing cesarean. Although obesity is clearly an operative risk factor, this study suggested that among obese gravidas, varying degrees of maternal obesity and accompanying medical complications, such as diabetes and hypertension, were not associated with greater operative morbidity. Furthermore, neither choice of skin incision nor type of anesthesia appeared to be related to operative morbidity. However, two factors potentially under the control of the clinician, increased length of surgery and operative blood loss, were associated significantly with measures of operative morbidity. A finding of worsened outcome with prophylactic antibiotics and heparin requires further study.