Genetic Abnormalities and Pregnancy Complications

Miscarriage - Also known as a spontaneous abortion, this is the loss of an embryo or fetus before it is viable (usually before 20 weeks). Miscarriage is common--in fact, one in five pregnancies end this way. Many happen before a woman knows she is pregnant and are thought to be late periods. Miscarriages can be caused by congenital anomalies (defective genes) or environmental damage during pregnancy.

Stillbirth - Spontaneous abortion or fetal death after 20 weeks gestation. These occur in less than 1% of all pregnancies.

Ecotopic pregnancy - Occurs when the fertilized egg implants somewhere outside the uterus (usually the fallopian tube). The growing fetus will eventually burst the organ that contains it, causing bleeding and risks to the mother’s life or future fertility.

Rh factor - All blood types (A, B, O, AB) are positive or negative depending on whether the Rh factor (a protein) is present or absent. About 85% of people are Rh positive (the factor is present) rather than Rh negative (absent). The Rh factor only affects pregnancies when the mother is Rh- and the father Rh+. If the resulting child is Rh+, the mother’s body may treat the baby as an intruder by developing antibodies to the Rh factor. This is only a problem in second and later pregnancies because antibodies produced during a first pregnancy attack the developing infant. But the problem is preventable if the mother receives a series of Rh-immune-globin shots during her first Rh+ pregnancy.

Genetic Abnormalities

These disorders can occur for a variety of reasons. They may be caused by extra chromosomes (such as Down syndrome, which is caused by an extra chromosome 21) or by other chromosomal mutations (such as fragile X syndrome or Huntington’s disease).

Defective genes may also be inherited from parents, resulting in a hereditary disease. Often healthy parents are unaware that they are carriers of a defective recessive gene. Cystic fibrosis is one of the most common genetic disorders, with approximately 5% of North Americans carrying at least one copy of the defective gene.

Some genetic disorders are X-linked, or carried on the X chromosome. When this is the case, females will not be affected since their other X chromosome is normal (although they can be carriers). Males, on the other hand, only have one X-chromosome and will be affected. Other genetic conditions may be such that a child will be affected even if only one of a pair of chromosomes is affected. One example is Praeder-Willi syndrome (associated with mental retardation, among other characteristics).

Hemophilia, a blood-clotting disorder, is a good example of an X-linked recessive condition. Only males are affected, while females can be carriers. The same Mendel square applies here.

Genetic counseling is for families who have genetic abnormalities or risks in their backgrounds. This counseling provides information for couples about the likelihood of passing on genetic disorders. Some genetic disorders affect only certain ethnic populations, such as sickle-cell anemia (8% of African Americans) or Tay-Sachs disease (common among Jews with European ancestry). Blood tests can identify whether parents are carriers of these and other disorders, although some genetic abnormalities cannot be identified so easily. Details on screening tests are forthcoming.

Prenatal Complications

Several pregnancy-related conditions can pose a risk to the health of mother and/or babies. Regular prenatal exams and tests screen for these and other abnormalities. The most common complications are:

• Pregnancy Induced Hypertension (PIH) and High Blood Pressure--Also called preeclampsia, this is the most common health problem to occur in pregnancy (7% of first-time mothers). Labor may be induced early if it poses an imminent health risk.
• Gestational Diabetes (GD)--High blood sugar (or glucose) levels during pregnancy. GD affects approximately 4% of women. Most women are screened for in the 28th week of pregnancy. Like PIH, labor is sometimes induced if needed.
• Placenta Previa--A condition where part or all of the placenta blocks the cervix. This happens in about 1 in 200 pregnancies and is detected through ultrasound. If the condition doesn’t disappear as the pregnancy progresses, a cesarean section may be necessary.
• Amniotic fluid abnormalities--These include Oligohydramnios (low amniotic fluid) or Polyhydramnios (high amniotic fluid), which can be found through ultrasound. Oligohydramnios is sometimes related to maternal hydration, but fluid levels also may drop prior to birth. About 1% of women will have Polyhydramnios.
• Preterm Labor--Uterine contractions at 20 to 37 weeks that are insufficient to dilate the cervix. This poses a serious but common pregnancy complication, which medical practitioners look for. Various drugs, bed rest, and other medical interventions can help carry the pregnancy as long as possible.
• Incompetent Cervix--A cervix is unable to stay closed during pregnancy, which can result in miscarriage or premature birth. Twenty to twenty-five percent of all second trimester losses are attributable to cervical incompetence. Stitches can be used to hold the weak cervix closed until the baby is sufficiently mature to be born.