Calendars, Clocks, and Choices.

The Post-term Baby

When the parents anxiously ask, "When will our baby be born?" I usually quip, "On its birthday!" Although this answer usually elicits a giggle, I am usually quite serious in my reply. When do we become concerned that the baby has not arrived at or around its expected due date?

We need to remember that the "expected date of delivery" is only an estimate of probable term gestation. Calculating the expected due date of delivery by last menstrual period may be of limited validity due to many factors. Many mothers are still nursing a previous infant when they suspect another pregnancy, and have not commenced regular menses. Some women are coming off of the use of birth control pills or injections of depo-provera, also causing unreliable landmarks for the purpose of dating conception.

All calculations are based upon a twenty-eight day cycle, which may be widely variable. The woman with a regular, thirty-four day cycle will ovulate later and come to term at a later date. This baby might just need to gestate a little longer; maybe she needs ten more brain cells to be the scientist who cures breast cancer!

There might also be another, social reason for the mother's misreporting of her LMP. A woman came to me very late in her pregnancy, having just arrived from Tiajuana, Mexico. She kept saying that her baby was due in another month. I told my friend Sol, who assisted me in translating for these women, that she would surely deliver by the weekend. We were certainly not surprised when her call came on the next day. As the baby (all ten pounds of him) was about to be born, the mother began crying and saying, "I am very worried because the baby is so premature!" As Sol translated this concern to me, I said, "I think that it is very important that this baby be early." We reassured the mom and dad that although the baby was probably quite early, that he was fat and healthy and that all would be well with him. The mother wept with joy as she held her beautiful newborn baby. I later discovered that when the mom became pregnant, she was in Tiajuana and Dad was in Santa Ana. So ... shoot me! It was none of my business.

It is important that after taking all of these factors into consideration, and carefully reassessing the possible due date, that we also differentiate between postdates and post-term.

As stated earlier, there may be many factors affecting date discrepancy, but there is also a very real post-term syndrome. Recent studies have concluded that true post-term babies have a higher morbidity and mortality rate, and may be at more risk than moderately preterm babies. Post-term syndrome appears with the following:

* Reduced placental function

* Reduction of amniotic fluid

* Nonmoldability of fetal skull (resulting in hypermolding, caput formation, and cephalohematoma)

There are higher risks of abruptio placenta, hypoglycemia and hypocalcemia, and hypoxia in labor. There is increased incidence of cephalo-pelvic disproportion resulting in instrumental delivery or cesarean section, shoulder dystocia, clavicle injuries, and brachial palsy. There is a much higher incidence of meconium staining, premature aspiration of meconium (in utero), meconium aspiration syndrome, and more reports of "failure to thrive" babies.

"Perinatal mortality is increased in post-term pregnancy.... Prolonged pregnancy is associated with an increased risk of intrapartum and neonatal death but not of antepartum death. The risk increases with the onset of labor. A high prevalence of meconium-stained amniotic fluid is an outstanding feature among the intrapartum and asphyxial neonatal deaths. The incidence of neonatal seizures, a marker of perinatal asphyxia, is between two and five times greater in infants born after forty-one weeks." (Enkin, Keirse, and Chalmers, A Guide to Effective Care in Pregnancy and Childbirth.)

It is important, therefore, that the midwife make as accurate an estimation of gestational age as possible in order to make appropriate care choices. If the expectant mother is very unsure of her dates, for whatever reason, it may be advisable to obtain an ultrasound. Remember that for purposes of dating, ultrasound results are less reliable after twenty weeks. I have found that fundal measurements (per centimeter) are often very close to actual weeks when done between sixteen and thirty-five weeks; I also find that adding exactly five months to the feeling of the first good kick by the mother is an amazingly good predictor. (Do not use the reported "butterfly kiss" but an unmistakable kick.)

There are several methods for determining fetal well-being when post-term babies are suspected. One method is to obtain a biophysical profile per ultrasound exam, which will offer information about the maturity of the placenta as well as amniotic fluid volume and bone maturity of the fetus. You may want to obtain a serum estriol level, another diagnostic for determining placental function. The mother can keep track of the number of fetal movements within a specified time, usually ten episodes within eight hours.

When it is established that true postmaturity is developing, every effort should be made to effect delivery. Careful monitoring of the fetus should be paramount, especially during second stage. If a homebirth, at the first sign of fetal distress, the mother should be transported to a hospital for delivery.

Nonviolent Induction

My recipe for term and beyond moms who are anxious for their babies to arrive is as follows: Tell them to go on a date with their partners, have a glass of wine with dinner, go home, and make love. Remind them that semen is a remarkably effective prostaglandin enhancer and can be very effective in ripening the cervix. It is amazing how well this prescription works!

--Val is a Certified Professional Midwife based in the Detroit, MI area