OBSTETRICS 1

A 28-year-old woman comes to your office for the first time for antenatal checkup, after having recently moved into your community. Her antenatal records show ultrasound performed at 16-weeks gestation, which was consistent with the date of last menstrual period. Now she is at 42-weeks gestation. On examination, fundal height is consistent with dates and the cervix is not favorable. Repeat ultrasonogram reveals a fetal weight of 3500g(7.7lb), and an amniotic fluid index of 10. Fetal heart tracing is reassuring. What is the most appropriate next step in management of this patient?
A. Twice weekly non-stress test and biophysical profile
B. Immediate induction of labor
C. Amnioinfusion and wait for spontaneous delivery
D. Cesarian section
E. Steroid administration and serial testing of fetal lung indices

Explanation:
Post-term pregnancy is defined as a pregnancy age more than 42-weeks gestation. Perinatal mortality is 2-3 times higher in post-term pregnancies and it is related most commonly to post-maturity syndrome, which occurs consequently to aging and infarction of the placenta. Post-mature infants typically have a loss of subcutaneous fat, long fingernails, dry and peeling skin, and abundant hair. In 70-80% of cases, fetuses are not affected by placental insufficiency and continue to grow past 42-weeks gestation, resulting in macrosomia. The cause of post-term pregnancy is unknown; however, some associated syndromes have been noted such as anencephaly and trisomy 18.

In terms of diagnosis of post-term pregnancy, the importance of accurate dating cannot be stressed enough. In fact 20-30% of pregnancies have uncertain dates, which may mislead to another diagnosis or cause it to be overlooked.

The management of post term pregnancy is principally based on the well being of the fetus. The non-stress test and biophysical profile should be performed twice weekly and if there is oligohydramnios or if spontaneous decelerations are noted, delivery has to be accomplished. If on the contrary, those parameters are reassuring, as in this case, labor should not be induced unless the cervix is favorable, the infant is macrosomic or in the presence of obstetrical indications for delivery. If the pregnancy is more than 43 weeks, delivery is mandated. If the pregnancy is more than 42 weeks, the cervix is favorable and fetal head is into the pelvis labor should be induced. Patients with uncertain dates should be managed expectantly as long as fetal assessment is reassuring, and the possibility of preterm pregnancy should be considered as much as that of post-term pregnancy.

Choice (B): Expectant management is more appropriate since fetal heart tracing is reassuring and there is no oligohydramnios. Moreover, the cervix is not favorable for induction of labor.

Choice (C): The patient does not have oligohydramnios (AFI of 5 or more), so amnioinfusion is not necessary.

Choice (D): C. Section is indicated in the presence of signs of fetal distress. The fetal heart activity of this fetus is normal.

Choice (E): Fetal lung maturity is not a concern here since it occurs in preterm not post-term infants. The respiratory condition most frequent in post term fetuses is meconium aspiration.