DIAGNOSIS AND ANTENATAL MANAGEMENT
Most multifetal pregnancies are diagnosed using ultrasound.
On a clinical basis, twin pregnancy should be suspected when the uterine size is large for the calculated gestational age.
A difference of 4 cm or more between the weeks of gesta-tion and the measured fundal height should prompt eval-uation with ultrasound to detect the cause (e.g., inaccurate gestational age, multiple gestation, hydramnios, gesta-tional trophoblastic disease, or pelvic tumor).
Serial ultrasound assessments have shown that only 50% of twin pregnancies detected in the first trimester result in the delivery of viable twins. The other 50% of cases deliver a single fetus because of intrauterine demise and ultimate resorption of one embryo/fetus (vanishing twin syndrome). During the first ultrasonographic exam-ination that confirms a twin gestation, chorionicity should be determined because the potential morbidity and mor-tality associated with a monochorionic gestation is differ-ent from that of a dichorionic gestation (described below). Chorionicity can be determined with almost 100% cer-tainty as early as 9 to 10 weeks of gestational age.
Once the diagnosis of twin pregnancy has been made and chorionicity has been assigned, subsequent antenatal care addresses each of the potential concerns for mother and fetus, as listed in Table 17.2. Although the maternal blood volume is greater with a twin gestation than with a singleton pregnancy, the anticipated blood loss at delivery is also greater. Anemia is more common in these patients, and a balanced diet during pregnancy, which may include increased intake of iron, folate, and other micronutrients, is important. Because of the increased risk for preterm labor inmultiple gestations, careful attention to detection of uterine con-tractions is important, and the patient should be cautioned about signs and symptoms of preterm labor, such as low back pain, a thin or increase in vaginal discharge, and vaginal bleeding. Cervical examinations to detect early effacement and dila-tion are often done every 1 to 2 weeks beginning in the midtrimester. When available, serial ultrasound assess-ments of endovaginal cervical length may be interspersed with the vaginal examinations.
Assessment of fetal fibronectin may aid in predicting preterm delivery in women, but it has limited predictive value in multifetal gestations.
At each visit, blood pressure should be evaluated and, if elevated, urine protein should be assessed. Beginning at 30 to 32 weeks, daily fetal kick counts are usually begun to help assess fetal well-being.
With multifetal gestations, periodic ultrasonographic exam-ination should be performed approximately every 4 weeks, begin-ning at 16 to 18 weeks of gestation. At each examination,growth of each fetus is assessed and an estimate of amniotic fluid volume is made. Discordant growth is defined as a 15% to 25% reduction in the estimated fetal weight of the small-est fetus compared with the largest. Ultrasonography should be performed more often in cases of discordant growth.