American Medical Association Family Medical Guide - American Medical Association [292]
Fraternal and identical twins
Fraternal twins result when two separate eggs are fertilized by two different sperm. Each twin gets nourishment from his or her own placenta. Identical twins result when a single egg that has been fertilized by one sperm divides into two identical embryos. Identical twins share a placenta.
A multiple pregnancy is usually discovered by a doctor during a routine prenatal examination and confirmed by ultrasound. The outlook is usually good for both the pregnant woman and the fetuses if the woman has adequate prenatal care, rest, and good nutrition. If you are having twins, your doctor may recommend that you take additional vitamin and mineral supplements throughout your pregnancy. Complications from multiple births can include anemia (see page 518), high blood pressure (see page 520), gestational diabetes (see page 521), preeclampsia (see below right), placenta previa (see next page), postpartum bleeding (see page 537), preterm labor (see page 529), and babies with low birth weight.
Polyhydramnios
Polyhydramnios (sometimes called simply hydramnios) is excess amniotic fluid in the uterus, a usually harmless condition that can occur in the middle to late stages of pregnancy. In most cases, the uterus swells only slightly more than normal and may cause no symptoms or only slight abdominal discomfort. The woman may feel slightly more breathless than usual or may have indigestion. In some cases, the abdominal swelling may be pronounced, stretching the skin over the abdomen. If polyhydramnios is severe, symptoms may begin suddenly and may be accompanied by nausea. Severe polyhydramnios can cause preterm labor (see page 529).
Polyhydramnios is more common in pregnancies that involve multiple fetuses (see previous page), in a woman who has diabetes (see page 889), or when a fetus has a malformation of the gastrointestinal system (such as a diaphragmatic hernia; see page 407) or of the spine or brain (such as a neural tube defect; see page 398).
Diagnosis and Treatment
If you have symptoms of polyhydramnios, your doctor may order a detailed ultrasound (see page 509) to rule out a fetal malformation or to detect a multiple pregnancy.
For a mild case of polyhydramnios, a doctor may recommend rest and may prescribe medication to relax the uterus and reduce the risk of preterm labor. In rare, severe cases, amniocentesis (see page 510) is performed to withdraw some of the excess fluid through a needle to reduce the pregnant woman’s discomfort; however, amniocentesis can bring on preterm labor.
Oligohydramnios
Oligohydramnios is a rare condition in which an abnormally small amount of amniotic fluid surrounds and cushions the fetus. The condition can result from severe preeclampsia (see below) in the woman, urinary abnormalities in the fetus, or a postterm pregnancy (see page 530). Early in pregnancy, oligohydramnios can cause a miscarriage. Late in pregnancy, it can cause deformities in the fetus or can be fatal to the fetus. If the amniotic fluid is not sufficient to cushion the fetus from pressure from the woman’s abdominal organs, the fetus can squeeze the umbilical cord against the wall of the uterus, cutting off its supply of oxygen and nutrients. In rare cases, the pressure of the uterus on the fetus can cause structural birth defects such as clubfoot (see page 402).
Treatment
If your doctor thinks you may have oligohydramnios, he or she will first try to treat the underlying disorder that has caused it, which is easier if it has resulted from preeclampsia rather than from an abnormality in the fetus. If your pregnancy is past the 37th week, your doctor may induce labor or perform a cesarean delivery (see page 534).
Preeclampsia and Eclampsia
Preeclampsia (also called toxemia of pregnancy or pregnancy-induced high blood pressure or hypertension)