Risk factors include preexisting maternal disorders (see Pregnancy Complicated by Disease), physical and social characteristics, age, problems in previous pregnancies (eg, spontaneous abortions), and problems that develop during the pregnancy (see Abnormalities of Pregnancy) or during labor and delivery (see Abnormalities and Complications of Labor and Delivery).

Hypertension

Pregnant women are considered to have chronic hypertension (CHTN) if hypertension was present before the pregnancy or if it develops before 20 wk of pregnancy. CHTN is differentiated from pregnancy-induced hypertension, which develops after 20 wk of pregnancy. In either case, hypertension is defined as systolic BP > 140 mm Hg or diastolic BP > 90 mm Hg on 2 occasions > 24 h apart. Hypertension increases risk of fetal growth restriction by decreasing uteroplacental blood flow. CHTN increases risk of preeclampsia to up to 50%. Poorly controlled hypertension increases risk of abruptio placentae by 2 to 10%.

Before attempting to conceive, women with hypertension should be counseled about the risks of pregnancy. If they become pregnant, prenatal care begins as early as possible and includes measurements of baseline renal function (eg, serum creatinine, BUN), funduscopic examination, and directed cardiovascular examination (auscultation, and sometimes with ECG, echocardiography, or both). Each trimester, 24-h urine protein, serum uric acid, serum creatinine, and Hct are measured. Ultrasonography to monitor fetal growth is done at 28 wk and every few weeks thereafter. Delayed growth is evaluated with multivessel Doppler testing by a maternal-fetal medicine specialist (for management of hypertension during pregnancy, see Pregnancy Complicated by Disease: Diagnosis and Treatment).

Diabetes

Diabetes mellitus occurs in 3 to 5% of pregnancies, but incidence will probably increase as the incidence of obesity increases.

Pregnant women with preexisting insulin-dependent diabetes are at increased risk of pyelonephritis, ketoacidosis, pregnancy-induced hypertension, fetal death, major fetal malformations, fetal macrosomia (fetal weight > 4.5 kg), and, if vasculopathy is present, fetal growth restriction. Insulin requirements usually increase during pregnancy.

Women with gestational diabetes are at risk of hypertensive disorders and fetal macrosomia. Gestational diabetes is routinely screened for at 24 to 28 wk or, if women have risk factors, also during the 1st trimester. Risk factors include previous gestational diabetes, a macrosomic infant in a previous pregnancy, family history of non-insulin–dependent diabetes, unexplained fetal losses, and body mass index (BMI) > 30 kg/m². A 50-g, 1-h glucose tolerance test is used. If the result is 140 to 200 mg/dL, a 2-h glucose tolerance test is done (see Table 2: Diabetes Mellitus and Disorders of Carbohydrate Metabolism: Diagnostic Criteria for Diabetes Mellitus and Impaired Glucose Regulation); if glucose is > 200 mg/dL or test results are abnormal, women are treated for the rest of the pregnancy with diet and, if necessary, insulin.

Good control of blood glucose during pregnancy almost eliminates the risk of adverse outcomes attributable to diabetes (for management of diabetes during pregnancy, see Pregnancy Complicated by Disease: During pregnancy).

Sexually transmitted diseases (STDs)

(see Sexually Transmitted Diseases (STD)) Fetal syphilis in utero can cause fetal death, congenital malformations, and severe disability. Risk of transmission of HIV from woman to offspring in utero or perinatally is 30 to 50% within 6 mo (see Human Immunodeficiency Virus (HIV): Transmission and Epidemiology; see Infections in Infants and Children: Human Immunodeficiency Virus (HIV) Infection in Children). During pregnancy, bacterial vaginosis, gonorrhea, and genital chlamydial infection increase risk of preterm labor and premature rupture of the membranes. Routine prenatal care includes screening tests for these infections at the 1st prenatal visit. Syphilis testing is repeated during pregnancy if risk continues and at delivery for all women. Pregnant women who have any of these infections are treated with antimicrobials.

Treatment of bacterial vaginosis, gonorrhea, or chlamydial infection may prolong the interval from rupture of the membranes to delivery and may improve fetal outcome by decreasing fetal inflammation. Treating HIV with zidovudine or nevirapine reduces risk of transmission by ²⁄₃; risk is probably lower (< 2%) with a combination of 2 or 3 antivirals (see Infections in Infants and Children: Prevention). These drugs are recommended despite potential toxic effects in the fetus and woman.

Pyelonephritis

Pyelonephritis increases risk of premature rupture of the membranes, preterm labor, and infant acute respiratory distress syndrome. Pregnant women with pyelonephritis are hospitalized for evaluation and treatment, primarily with urine culture plus sensitivities, IV antibiotics (eg, a 3rd-generation cephalosporin with or without an aminoglycoside), antipyretics, and hydration. Pyelonephritis is the most common nonobstetric cause of hospitalization during pregnancy. Oral antibiotics specific to the causative organism are begun 24 to 48 h after fever resolves and continued until the total course of antibiotic therapy is 7 to 10 days. Prophylactic antibiotics (eg, nitrofurantoin, trimethoprim-sulfamethoxazole) with periodic urine cultures are continued for the rest of the pregnancy.

Acute surgical problems

Major surgery, particularly intra-abdominal, increases risk of preterm labor and fetal death. Also, physiologic changes of pregnancy make intra-abdominal disorders that require surgery (eg, appendicitis, cholecystitis, intestinal obstruction) difficult to recognize, often delaying diagnosis and thus worsening outcomes. After surgery, antibiotics and tocolytic drugs are given for 12 to 24 h. If nonemergency surgery is necessary during pregnancy, it is most safely done during the 2nd trimester.

Genital tract abnormalities

Structural abnormalities of the uterus and cervix (eg, uterine septum, bicornuate uterus) make fetal malpresentation, dysfunctional labor, and the need for cesarean section more likely. Uterine fibroids can cause placental abnormalities and may grow rapidly or degenerate during pregnancy; degeneration often causes severe pain and peritoneal signs. Cervical incompetence (see Abnormalities of Pregnancy: Cervical Incompetence) makes preterm delivery more likely. In women who have had full-thickness myomectomy, vaginal delivery may result in uterine rupture and thus should be avoided. Uterine abnormalities that lead to poor obstetric outcomes often require surgical correction, which is not done during pregnancy.

Maternal age

Teenagers, who account for 13% of all pregnancies, tend to neglect prenatal care. The result is an increased incidence of preeclampsia, preterm labor, and anemia, which often leads to fetal growth restriction.

In women > 35, the incidence of preeclampsia is increased, as is that of gestational diabetes, dysfunctional labor, abruptio placentae, stillbirth, and placenta previa. These women are also more likely to have preexisting disorders (eg, CHTN, diabetes). Because risk of fetal chromosomal abnormalities increases as maternal age increases, genetic testing should be considered (see Prenatal Genetic Counseling and Evaluation: Genetic Evaluation).

Maternal weight

Pregnant women whose BMI was < 19.8 kg/m² before pregnancy are considered underweight, which predisposes to low birth weight (< 2.5 kg) neonates. Such women are encouraged to gain about 12.5 to 18 kg during pregnancy.

Pregnant women whose BMI was > 29.0 kg/m² before pregnancy are considered overweight, making maternal hypertension and diabetes, postterm pregnancy, fetal macrosomia, and the need for cesarean section more likely. Such women are encouraged to limit weight gain during pregnancy to < 7 kg.

Exposure to teratogens

Common teratogens (agents that cause fetal malformation) include infections, drugs, and physical agents. Malformations are most likely to result if exposure occurs between the 2nd and 8th wk after conception (the 4th to 10th wk after the last menstrual period), when organs are forming. Other adverse pregnancy outcomes are also more likely. Pregnant women exposed to teratogens are counseled about increased risks and referred for detailed ultrasound evaluation to detect malformations.

Common infections that may be teratogenic include herpes simplex, viral hepatitis, rubella, varicella, syphilis, toxoplasmosis, and cytomegalovirus and coxsackievirus infections.

Commonly used drugs that may be teratogenic include alcohol, tobacco, and some anticonvulsants, antibiotics, and antihypertensives (see Table 2: Normal Pregnancy, Labor, and Delivery: Known or Suspected Teratogens).

Cigarette smoking is the most common addiction among pregnant women. Also, percentages of women who smoke and of those who smoke heavily appear to be increasing. Only 20% of smokers quit during pregnancy. Carbon monoxide and nicotine in cigarettes cause hypoxia and vasoconstriction, increasing risk of spontaneous abortion (fetal loss or delivery < 20 wk), fetal growth restriction (birth weight averaging 170 g less than that of neonates whose mothers do not smoke), abruptio placentae, placenta previa, premature rupture of the membranes, preterm birth, chorioamnionitis, and stillbirth. Neonates whose mothers smoke are also more likely to have anencephaly, congenital heart defects, orofacial clefts, sudden infant death syndrome, deficiencies in physical growth and intelligence, and behavioral problems. Smoking cessation or limitation reduces risks.

Alcohol is the most commonly used teratogen. Drinking alcohol during pregnancy increases risk of spontaneous abortion. Risk is probably related to amount of alcohol consumed, but no amount is known to be risk-free. Regular drinking decreases birth weight by about 1 to 1.3 kg. Binge drinking in particular, possibly as little as 45 mL of pure alcohol (equivalent to about 3 drinks) a day, can cause fetal alcohol syndrome. This syndrome occurs in 2.2/1000 live births; it includes fetal growth restriction, facial and cardiovascular defects, and neurologic dysfunction. It is a leading cause of mental retardation and can cause neonatal death due to failure to thrive.

Cocaine use has indirect risks (eg, maternal stroke or death during pregnancy). It also directly causes fetal vasoconstriction and hypoxia. Repeated use increases risk of spontaneous abortion, fetal growth restriction, abruptio placentae, preterm birth, stillbirth, and congenital malformations (eg, CNS, GU, and skeletal malformations; isolated atresias).

Although marijuana's main metabolite can cross the placenta, recreational use of marijuana use does not consistently appear to increase risk of congenital malformations, fetal growth restriction, or postnatal neurobehavioral abnormalities.

Prior stillbirth

Causes of stillbirth (fetal death > 20 wk) may be maternal, placental, or fetal (see Abnormalities of Pregnancy: Stillbirth). Having had a stillbirth increases risk of fetal death in subsequent pregnancies. Fetal surveillance using antepartum testing (eg, nonstress testing, biophysical profile) is recommended. Treatment of maternal disorders (eg, CHTN, diabetes, infections) may lower risk of stillbirth in a current pregnancy.

Prior preterm delivery

Previous preterm delivery due to preterm labor increases risk of future preterm deliveries; if the previous preterm neonate weighed < 1.5 kg, risk of preterm delivery in the next pregnancy is 50%. Causes of preterm delivery include multifetal (multiple) pregnancy, preeclampsia or eclampsia, placental abnormalities, preterm rupture of the membranes (causing ascending uterine infection), pyelonephritis, some STDs, and spontaneous preterm labor. Women with prior preterm labor and delivery require ultrasound evaluation, including measurement of cervical length (see Abnormalities of Pregnancy: Cervical Incompetence), at 16 to 18 wk and should be monitored closely for pregnancy-induced hypertension. If symptoms of preterm labor develop, uterine contraction monitoring, testing for bacterial vaginosis, and fetal fibronectin measurement may identify women who need closer observation by their physician.

Prior neonate with a genetic or congenital disorder

Risk of a having a fetus with a chromosomal disorder is increased for most couples who have had a fetus or neonate with a chromosomal disorder (recognized or missed—see Prenatal Genetic Counseling and Evaluation: Risk factors). Recurrence risk for most genetic disorders is unknown. Most congenital malformations are multifactorial; risk of having a subsequent fetus with malformations is ≤ 1%. If couples have had a neonate with a genetic or chromosomal disorder, genetic screening is indicated. If couples have had a neonate with a congenital malformation, high-resolution ultrasonography and evaluation by a maternal-fetal medicine specialist is indicated.

Hydramnios (polyhydramnios) and oligohydramnios

Hydramnios (excess amniotic fluid) can lead to severe maternal shortness of breath and preterm labor. Risk factors include uncontrolled maternal diabetes, multifetal pregnancy, isoimmunization, and fetal malformations (eg, esophageal atresia, anencephaly, spina bifida).

Oligohydramnios (deficient amniotic fluid) often accompanies congenital malformations of the fetal urinary tract and severe fetal growth restriction (< 3rd percentile). Also, Potter's syndrome with pulmonary hypoplasia or fetal surface compression abnormalities may result, usually in the 2nd trimester, and cause fetal death.

Hydramnios and oligohydramnios are suspected if uterine size does not correspond to gestational date or may be discovered incidentally via ultrasonography, which is diagnostic.

Multifetal (multiple) pregnancy

Multifetal pregnancy increases risk of fetal growth restriction, preterm labor, abruptio placentae, congenital malformations, perinatal morbidity and mortality, and, after delivery, uterine atony and hemorrhage (see Abnormalities and Complications of Labor and Delivery: Postpartum Hemorrhage). Multifetal pregnancy is detected during routine ultrasonography at 18 to 20 wk.

Prior birth injury

Birth of a neonate with a delivery-related injury (eg, cerebral palsy, developmental delay or trauma due to forceps or vacuum extractor delivery, shoulder dystocia with Erb-Duchenne paralysis) does not increase risk in future pregnancies. However, the prior delivery records should be assessed for modifiable risk factors that may have predisposed to the injury.

Last full review/revision November 2005