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Risk Factors for Complications During Pregnancy

by Raul Artal, MD

Risk factors include

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 gestational 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 and risk of adverse fetal and maternal outcomes (see Hypertension in Pregnancy).

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 evaluation (auscultation and sometimes 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 4 wk thereafter. Delayed growth is evaluated with multivessel Doppler testing by a maternal-fetal medicine specialist (for management of hypertension during pregnancy, see Treatment).

Diabetes

Overt diabetes mellitus occurs in ≥ 6% of pregnancies, and gestational diabetes occurs in about 8.5% of pregnancies. Incidence is increasing as the incidence of obesity increases.

If pregnant women have preexisting insulin -dependent diabetes, risk is increased for pyelonephritis, ketoacidosis, preeclampsia, 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.

If women have gestational diabetes, risk of hypertensive disorders and fetal macrosomia is increased. Gestational diabetes is routinely screened for at 24 to 28 wk and, if women have risk factors, 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/m 2 . The diagnosis of gestational diabetes is made based on results of oral glucose tolerance test (OGTT—see Table: Threshold Values of Plasma Glucose for Diagnosing* Gestational Diabetes Mellitus Using the 100-g Oral Glucose Tolerance Test), although some practitioners first do a random plasma glucose test to check whether the diagnosis is possible. In the US, most practitioners do 50-g glucose challenge screening, and if any plasma glucose measurement is > 130 mg/dL but < 200 mg/dL, they do a 100-g OGTT. In Europe and elsewhere, a one-step 2-h 75-g OGTT is used; glucose is measured after a fast and 2 h after glucose is given.

Threshold Values of Plasma Glucose for Diagnosing* Gestational Diabetes Mellitus Using the 100-g Oral Glucose Tolerance Test

100-g OGTT

NDDG

Carpenter and Coustan

Timing

of Test

Plasma Glucose (mg/dL)

Fasting

105

95

1-h

190

180

2-h

165

155

3-h

145

140

*Gestational diabetes is diagnosed when at least 2 threshold values are met or exceeded.

The Carpenter and Coustan criteria are used by some clinicians (Carpenter MW, Coustan DR: Criteria for screening tests for gestational diabetes. American Journal of Obstetrics and Gynecology 144 (7): 768–773, 182.

Fasting is required whenever clinicians suspect that patients have undiagnosed diabetes to avoid giving them an unnecessary load of glucose.

NDDG = National Diabetes Data Group; OGTT = oral glucose tolerance test.

Optimal treatment of gestational diabetes (with dietary modification, exercise, and close monitoring of blood glucose levels and insulin when necessary—see Monitoring) reduces risk of adverse maternal, fetal, and neonatal outcomes.

Threshold Values for Diagnosing Overt Diabetes in Pregnancy

Test*

Threshold Value

Fasting plasma glucose

126 mg/dL

HbA 1C

6.5%

Random plasma glucose

200 mg/dL on > 1 occasion

*Fasting plasma glucose and Hb A 1C are measured if clinicians suspect diabetes (eg, in patients with risk factors, such as obesity, a strong family history of diabetes, or a history of gestational diabetes in a previous pregnancy).

HbA 1c = glycosylated Hb.

Sexually transmitted diseases (STDs)

(See Overview of Sexually Transmitted Diseases.) 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) Infection : Transmission; see Human Immunodeficiency Virus (HIV) Infection in Infants and 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 first 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 two thirds; risk is probably lower (< 2%) with a combination of 2 or 3 antivirals (see Human Immunodeficiency Virus (HIV) Infection 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 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 to complete the whole course of antibiotic therapy, usually 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. However, surgery is usually tolerated well by pregnant women and the fetus when appropriate supportive care and anesthesia (maintaining BP and oxygenation at normal levels) are provided, so physicians should not be reluctant to operate; delaying treatment of an abdominal emergency is far more dangerous.

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 delivery more likely. Although unlikely, uterine fibroids can cause placental abnormalities (eg, placenta previa), preterm labor, and recurrent spontaneous abortion. Fibroids may grow rapidly or degenerate during pregnancy; degeneration often causes severe pain and peritoneal signs. Cervical insufficiency (incompetence—see Cervical Insufficiency) makes preterm delivery more likely. If, before pregnancy, women have had a myomectomy in which the uterine cavity was entered, cesarean delivery is required because uterine rupture is a risk during subsequent vaginal delivery. Uterine abnormalities that lead to poor obstetric outcomes often require surgical correction, which is done after delivery.

Maternal age

Teenagers, who account for 13% of all pregnancies, have an increased incidence of preeclampsia, preterm labor, and anemia, which often leads to fetal growth restriction. The cause, at least in part, is that teenagers tend to neglect prenatal care, frequently smoke, and have higher rates of sexually transmitted diseases.

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 offered (see Genetic Evaluation).

Maternal weight

Pregnant women whose BMI was < 19.8 kg/m 2 before pregnancy are considered underweight, which predisposes to low birth weight (< 2.5 kg) in neonates. Such women are encouraged to gain at least 12.5 kg during pregnancy.

Pregnant women whose BMI was > 29.0 kg/m 2 before pregnancy are considered overweight, making maternal hypertension and diabetes, postterm pregnancy, fetal macrosomia, preeclampsia, and the need for cesarean delivery more likely. Such women are encouraged to limit weight gain during pregnancy to < 11.5 kg.

Maternal height

Short (about < 152 cm) women are more likely to have a small pelvis, which can lead to dystocia with fetopelvic disproportion or shoulder dystocia. For short women, preterm labor and intrauterine growth restriction are also more likely.

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 cocaine ( Drugs in Pregnancy : Social and Illicit Drugs) and some prescription drugs (see Some Drugs With Adverse Effects During Pregnancy).

Prior stillbirth

Stillbirth is delivery of a dead fetus at > 20 wk gestation. Fetal death during late pregnancy may have maternal, placental, or fetal anatomic or genetic causes (see Common Causes of Stillbirth). Having had a stillbirth or late abortion (ie, at 16 to 20 wk) increases risk of fetal death in subsequent pregnancies. Degree of risk varies depending on the cause of a previous stillbirth. 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

Preterm delivery is delivery before 37 wk (see Preterm Labor). 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%. Women with prior preterm delivery due to preterm labor should be closely monitored at 2-wk intervals after 20 wk. Monitoring includes

  • Ultrasound evaluation, including measurement of cervical length and shape, at 16 to 18 wk

  • Uterine contraction monitoring

  • Testing for bacterial vaginosis

  • Measurement of fetal fibronectin

Women with prior preterm birth due to preterm labor or with shortening (< 25 mm) or funneling of the cervix should be given 17 α-OH-progesterone 250 mg IM once/wk.

Prior neonate with a genetic or congenital disorder

Risk of 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 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 recommended. If couples have had a neonate with a congenital malformation, genetic screening, high-resolution ultrasonography, and evaluation by a maternal-fetal medicine specialist is recommended.

Polyhydramnios (hydramnios) and oligohydramnios

Polyhydramnios (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 syndrome with pulmonary hypoplasia or fetal surface compression abnormalities may result, usually in the 2nd trimester, and cause fetal death.

Polyhydramnios 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 Postpartum Hemorrhage). Multifetal pregnancy is detected during routine ultrasonography at 18 to 20 wk.

Prior birth injury

Most cerebral palsy and developmental delay is caused by factors unrelated to a birth injury. Injuries such as brachial plexus damage can result from procedures such as forceps or vacuum extractor delivery but often result from intrauterine forces during labor or malposition during the last weeks of pregnancy. Previous shoulder dystocia is a risk factor for future dystocia, and the delivery records should be reviewed for potentially modifiable risk factors (eg, fetal macrosomia, operative vaginal delivery) that may have predisposed to the injury.

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Drugs Mentioned In This Article

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  • RETROVIR
  • VIRAMUNE
  • FURADANTIN, MACROBID, MACRODANTIN
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  • CRINONE

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