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The goals of prenatal care are to assess pregnancy and fetal risks and to monitor the pregnancy to optimize the chances for a good outcome. Ideally, a pregnancy is planned, and counseling and health assessments can begin before the fetus is conceived. There are risk assessment tools for evaluating the mother’s family and medical history, previous pregnancy history, and the progress of this pregnancy.1 Currently, most women receive a level 1 fetal ultrasound before 20 weeks’ gestation to assess gestational age, screen the fetus for anomalies, determine placental position, and identify multiple births. A level 1 ultrasound obtained prior to 20 weeks is more accurate than the date of the last menstrual period to determine gestational age. The early screening ultrasound is not intended to identify more subtle structural abnormalities. If anomalies are noted, the woman will be referred for a complete ultrasound evaluation of the fetus using more sensitive equipment and expert evaluations. In the United States it is now unusual for infants to deliver with major skeletal, cardiac, or other internal organ structural anomalies that have not been identified prior to delivery. Common chromosome anomalies such as trisomy 21 also have structural signatures that can be identified by early gestational ultrasound. The genetic abnormality then can be verified by amniocentesis. An accurate early assessment of gestational age is the cornerstone for subsequent monitoring of the pregnancy and decisions about the timing of delivery.

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All women should have plasma tests to evaluate blood type and Coombs status. Women who are Rh negative are carefully followed and given anti-Rh antibodies for fetal loss and for pregnancy abnormalities that may be associated with bleeding. The maternal plasma also is tested for antibodies to syphilis, rubella, hepatitis B, and often human immunodeficiency virus (HIV), as these infectious diseases adversely affect the fetus. Women are routinely offered second-trimester antenatal screening for Down syndrome using 3 analytes in maternal plasma, called the triple screen.2 Women at high risk of having a fetus with Down syndrome will have low α-fetoprotein, high human chorionic gonadotrophin, and low unconjugated estriol levels, adjusted for gestational age. If the maternal plasma tests indicate increased risk, a level 2 ultrasound can identify structural findings frequently associated with Down syndrome: increased nuchal fold translucency, a hypoplastic fetal nasal bone, and a short length relative to head size, together with other findings. The diagnosis can be confirmed by karyotype of fetal cells from amniotic fluid. The risk of Down syndrome increases with maternal age, and a fetal chromosome assessment is recommended for pregnant women 35 years or older.

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Maternal serum α-fetoprotein values also are used to screen pregnancies for neural tube defects. In contrast to Down syndrome, this protein is elevated with open neural tube defects as well as with abdominal wall defects such as omphalocele or gastroschisis. Specific genetic screening is offered to women on the basis of family history and racial background. These tests can be performed on the ...

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