Pregnancy and Advanced Maternal Age

December 14, 2007

"Advanced" maternal age is defined as any expectant mother who will have made her 35th birthday by the time she delivers. This term is a throw-back to the times when women married in their teens and began giving birth at a much younger age.

In modern times, with women playing important roles in the marketplace alongside men and putting off their families for business or personal reasons, the magic number of 35 still stands as a turning point in prenatal surveillance, because this begins a high-risk group with their own set of risk factors besides all of the other risks of pregnancy and delivery.

Down Syndrome

At 40, the chance of Down Syndrome is 1 in 109. Age 35 has been recommended as the age at which aggressive screening be done via ultrasound and possibly amniocentesis or chorionic villous sampling. It's important, though, to factor in whether you'd do anything with the information. (Women who would never consider an abortion, no matter what, might not want to subject a probably normal baby to the very small risks associated with the invasive procedures.)

From Hook and Lindsjo: American Journal of Human Genetics, Vol. 30, 1998, come the
following odds of Down Syndrome based on age:
At Age: 30 31 32 33 34 35 36 37 38 39
The Risk of Down Syndrome is 1 in: 885 826 725 592 465 365 287 225 176 139
At Age: 40 41 42 43 44 45 46 47 48 49
The Risk of Down Syndrome is 1 in: 109 85 67 53 41 32 25 20 16 12

It makes sense that chromosomal problems go up with advancing maternal age, because the egg a woman conceives with is as old as she is. Every woman was born with all of the eggs she ovulates with for the rest of her post-pubescent, pre-menopausal life. So if you're 30, and your Mom was 30 when she conceived you, then you're the product of an egg that developed 60 years ago!

Before you think that you sure are lookin' good for 60, remember the sobering aspect of all of this--the older you are, the older your eggs and their chromosomes are--this is the reason for age-related risk.

The sperm, on the other hand, are young whipper-snappers, so they don't play a role in the risk of Down Syndrome as related to paternal age. The father's age, however, will influence the chances of other genetic (autosomal dominant) diseases, like Marfan Syndrome, Huntington Chorea, and von Willebrand Disease.

Pregnant With Twins

Identical (monozygotic, or twinning from a single egg--"identical") twins happens once in 250 pregnancies. This is unaffected by age, race, or any other factors. Dizygotic twins (twins from fertilization of two eggs), however, is a different story.

In dizygotic, or "fraternal," twins, not only maternal age, but the number of previous pregnancies ("parity"), increases the chances of twins. Twins are three times as high in women over 35 with at least four other children than women under twenty pregnant for the first time. Taking parity alone, the chance of twins doubles from the first pregnancy to the fourth pregnancy. Racially, African-American women have a 1 out of 79 chance of twins; caucasian women 1 out of a hundred; Asian women more rarely--1 in 155 pregnancies. When women first get off of the birth control pill, their pituitary glands crank back up with higher amounts of stimulation than usual, so the chance of twins is greater with conception the first month off of the pill. Now that ultrasound is being done routinely at earlier gestational periods, it is becoming obvious that the occurrence of twins may be higher than what are actually observed. The phenomenon of the "absorbed twin," has been observed to happen more frequently than once thought. Occasionally, one of the twins doesn't make it, miscarrying silently, then getting absorbed. This may present as bleeding in the first trimester, labeled as a "threatened" miscarriage. Fetal death even near the end of the first trimester may be hidden, showing no evidence of any signs at the time of the delivery of the single baby at term.

Other Maternal Pregnancy Risks

There is an increased tendency to Pregnancy-induced Hypertension with later pregnancies. Also, gestational diabetes, placental abruption, and even some diastrous events like stroke. But as there has been an increased prevalence of pregnancies over 35, so too there has been a respect for increased vigilence. Today, obstetricians aren't particularly fearful of a woman pregnant in her later thirties--they have their special set of risk factors just like teenagers who are pregnant have risks unique to them.

Besides Down Syndrome, other genetic problems can be diagnosed prenatally with sampling via chorionic villous sampling (CVS) or amniocentesis. CVS, usually done around 10 weeks gestation, involves getting a biopsy of non-fetal pregnancy tissue by a needle through the cervix. Amniocentesis is drawing away fluid for study from the amniotic sac--through the mother's abdomen.

Invasive Prenatal Diagnosis

Theoretically there are genetic problems of anatomy or metabolism that may make prenatal treatment possible if diagnosed by amniocentesis, but for the most part, amniocentesis is offered routinely on women 35 and older to diagnose those age-related genetic problems for which abortion is the only "remedy." A pro-life stance means that a patient may base her decision on whether to have one or not on philosophical grounds.

The chances of miscarrying are very low with amniocentesis, and every doctor has a unique rate--a woman should ask her doctor what his or hers is--usually about 0.5-2%. This means that there's a 1 in 200 chance at best, or a 1 in 50 chance at worst that she might accidentally miscarry a normal child with routine genetic amniocentesis. Often this risk is greater than the risk of a genetically affected baby, the risk TO a normal baby greater than the chances OF an abnormal baby. People who aren't opposed to abortion (pro-choice) say that although this may be true, still the reality of a genetic problem is such a devastation as to be unacceptable.

Amniocentesis--drawing away a volume of amniotic fluid by inserting a needle, usually guided with ultrasound, through the mother's skin where it crosses the uterine wall into then amniotic sac where the baby and fluid reside. It is most often done in the third trimester to test for lung maturity when there is a danger in allowing a high-risk pregnancy to continue and at 15 weeks to do genetic testing.

Chorionic Villous Sampling (CVS)--this technigue uses a needle through the cervix (a vaginal approach) to biopsy some chorionic tissue (placental tissue). The cells retrieved can be tested for genetic abnormalities, yielding the same information that amniocentesis provides, but over a month earlier.

(Interestingly, even pro-life couples sometimes accept an amniocentesis purely for reassurance or alternately to prepare themselves ahead of time for their child and the problems that will come.)

There is a big difference between a medically necessary procedure and a medically recommended procedure. Pregnancy is a risk, always; it is a biological gamble, with accidental outcomes sometimes occurring even with the best of care. Medical science has now advanced to the point where a bad genetic result can be eliminated. But that is the medical and technological reality. The philosophical reality is a personal position on the part of the prospective parents and should be taken into account as well. The recommendation by a doctor is a medical recommendation, and negligent malpractice could be alleged were he or she not to let a patient know amniocentesis is available and "medically" recommended. Whether pro-choice or pro-life, a doctor is obligated to inform the expectant couple of their choices as part of routine and proper prenatal care. But if there are philosophical positions they can't deviate from, it becomes their call--medically, ethically, legally, and intellectually.

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