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Family Health Magazine - CHILDBIRTH

Delaying Motherhood
With pregnancy, timing is important

In the recent past, the majority of women became pregnant in their most fertile years, their mid-20s. Today, more women decide to get post-secondary education and work outside the home first. Pregnancy is put off until age 30 or 40. While every pregnancy is unique, age can have a tremendous effect on the ease of pregnancy and delivery. Advanced maternal age is defined as pregnancy occurring at or over the age of 35.

Many women realize that it is more difficult to become pregnant as they age. Older women are more likely to miscarry (lose the pregnancy). The risk of chromosomal disorders like Down syndrome also climbs. However, many women do not know that becoming pregnant at an older age increases the risk of pregnancy complications. These include high blood pressure, diabetes, multiple birth, placenta previa, caesarean delivery, stillbirth, and preterm (early) delivery.

Reduced fertility

Most women are aware that their biological clock is ticking. However, many believe that advanced reproductive technologies (ART, commonly known as fertility treatment) will be a magic bullet. They think ART will provide a solution well into their 40s. However, ART does have limitations. Age is the most important factor when it comes to conception, as it affects both the number and the quality of eggs. The ability to become pregnant is significantly lower at age 37. Women between 35 and 37 years old who have been trying to become pregnant for six months or more should be referred for fertility assessment. Women over 37 years old should be referred earlier. The initial fertility assessment will also include a work up for male factors that can play a role in conceiving including low sperm count and poor sperm quality.

Chromosomal disorders

At age 25, a pregnant woman has one chance in 1,500 of having an infant with a chromosomal disorder. At age 34, the chances are one in 172. At age 40, the risk increases to a one in 40 chance.

All pregnant women in Canada, regardless of age, should be offered genetic screening. Woman over the age of 35 years old should be offered additional genetic screening. This should include:

• a first trimester nuchal translucency screen (FTS), done between 11 and 13 weeks, or
• a maternal serum screen (MSS), done between 15 and 20 weeks.

These screening tests look at risks of trisomy 21 (Down syndrome), trisomy 18, and trisomy 13. The MSS also gives a risk score for neural tube defects (problems with how the brain or spinal cord are formed).

Genetic screening is only a screening tool. If it is positive, further testing can confirm that the problem exists. These extra tests take samples of the amniotic fluid (amniocentesis), or samples from the placenta (chorionic villus sampling or CVS) to determine the actual genetic risk. The possibility of miscarriage is the major risk of invasive prenatal testing like amniocentesis (about one in 200) and CVS (one in 100).

The benefit of CVS is that it can be carried out earlier than amniocentesis. This provides information about genetic results earlier in the pregnancy, at 11 weeks versus 15 weeks for amniocentesis.

The new non-invasive prenatal testing (NIPT) is a very accurate screening tool for detecting Down syndrome. It finds 99 per cent of cases. The NIPT only requires the mother to have a blood test. It finds the baby’s DNA in the mother’s blood stream. It does have a false positive rate of 0.2 per cent. This means that one in 500 pregnancies will be normal but will have a positive result. As with other screening tests, additional tests will be needed to confirm any genetic issue. The main advantage is that there is no risk of miscarriage or other complications with the procedure. The biggest drawback of the NIPT is the expense. In Canada, it costs about $800. This is not covered by most third party health insurance plans.

Miscarriage rates

Miscarriage rates increase with advancing maternal age. For women in their 20s, 10 per cent of pregnancies end in miscarriage. The rate for women between the ages of 35 and 39 is about 20 per cent. The rate increases to 35 per cent for women ages 40 to 44.

If you are older and have had repeated miscarriages, talk to your doctor before getting pregnant again. Certain treatments may reduce the risk of recurrent miscarriage in some women.

Pregnancy complications

Women of advanced maternal age have a higher incidence of gestational diabetes, early delivery, low birth weight and genetic defects.

The risk of developing gestational diabetes is three times greater for women over age 40. Maintaining a healthy weight, and eating a lower carbohydrate and low sugar diet helps lower the risk. Women should also exercise regularly, for at least 120 minutes a week.

The Society of Obstetricians and Gynacologists of Canada reports:

• half of first time mothers over age 40 require a caesarean section, compared with 25 per cent of women aged 20 to 24
• the risk of chromosomal disorders is four times higher in women 35 years or older than in women aged 20 to 34
• rates of preterm birth are 20 per cent higher in women 35 years or older than in women aged 20 to 34
• the risk of low birth weight is seven per cent higher in women 35 years or older than in women aged 20 to 34.

Reducing the risk of preterm birth starts with not being underweight when becoming pregnant. Gaining an appropriate amount of weight and avoiding alcohol, cigarettes and drugs during pregnancy are also key.

Not all preterm births can be prevented, but a healthy start helps. If you have already had a baby born before term, talk to your doctor about what you can do. Ultrasounds to determine the length of the cervix and progesterone supplementation might be of benefit.

It is true that women are less fertile and have a higher risk of complications as they age. However, older women can still have a healthy pregnancy and delivery. Focusing on good health before and during pregnancy makes a big difference at any age.

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