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Risk Factors for Complications During Pregnancy

by Raul Artal, MD

Risk factors for complications during pregnancy include


Pregnant women are considered to have chronic hypertension (CHTN) if

  • Hypertension was present before the pregnancy

  • Hypertension 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 the following:

  • Fetal growth restriction (by decreasing uteroplacental blood flow)

  • Adverse fetal and maternal outcomes

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 Other Heart Disorders in Pregnancy : Treatment).


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.

Preexisting insulin -dependent diabetes increases the risk of the following:

  • Pyelonephritis

  • Ketoacidosis

  • Preeclampsia

  • Fetal death

  • Major fetal malformations

  • Fetal macrosomia (fetal weight > 4.5 kg)

  • If vasculopathy is present, fetal growth restriction

Insulin requirements usually increase during pregnancy.

Gestational diabetes increases the risk of the following:

  • Hypertensive disorders

  • Fetal macrosomia

Gestational diabetes is routinely screened for at 24 to 28 wk and, if women have risk factors, during the 1st trimester. Risk factors include the following:

  • Previous gestational diabetes

  • A macrosomic infant in a previous pregnancy

  • Family history of non- insulin –dependent diabetes

  • Unexplained fetal losses

  • Body mass index (BMI) > 30 kg/m 2

Some practitioners first do a random plasma glucose test to check whether gestational diabetes is possible. However, screening and confirmation of the diagnosis of gestational diabetes is best based on results of the 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). Based on a recommendation from the 2013 National Institutes of Health (NIH) consensus development conference, screening begins with a 1-h 50-g glucose load test (GLT); if results are positive (plasma glucose > 135 mg/dL), a 3-h 100-g OGTT is done.

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

100-g OGTT


Carpenter and Coustan


of Test

Plasma Glucose (mg/dL)













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

Vandorsten JP, Dodson WC, Espeland MA, et al. National Institutes of Health (NIH) Consensus Development Conference Statement: Diagnosing gestational diabetes mellitus. NIH Consensus State-of-the-Science Statements 29:1–31, 2013.

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) reduces risk of adverse maternal, fetal, and neonatal outcomes.

Threshold Values for Diagnosing Overt Diabetes in Pregnancy


Threshold Value

Fasting plasma glucose

126 mg/dL

HbA 1C


Random plasma glucose

200 mg/dL on > 1 occasion

*Fasting plasma glucose and HbA 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.

Women with gestational diabetes mellitus may have had undiagnosed diabetes mellitus before pregnancy. Thus, they should be screened for diabetes mellitus 6 to 12 wk postpartum, using the same testing and criteria used for patients who are not pregnant.

Sexually Transmitted Diseases (STDs)

Fetal syphilis in utero can cause fetal death, congenital malformations, and severe disability.

Without treatment, risk of transmission of HIV from woman to offspring is about 30% prepartum and about 25% intrapartum. Neonates are given antiretroviral treatment within 6 h of birth to minimize risk of transmission intrapartum (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.

Giving zidovudine or nevirapine to pregnant women with HIV infection 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 increases risk of the following:

  • Premature rupture of the membranes

  • Preterm labor

  • Infant respiratory distress syndrome

Pyelonephritis is the most common nonobstetric cause of hospitalization during pregnancy.

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. 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 the following:

  • Preterm labor

  • 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 the following more likely:

  • Fetal malpresentation

  • Dysfunctional labor

  • The need for cesarean delivery

Uterine fibroids uncommonly 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) 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.

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 25 to 29.9 kg/m 2 (overweight) or ≥ 30 (obese) before pregnancy are at risk of maternal hypertension and diabetes, postterm pregnancy, pregnancy loss, fetal macrosomia, congenital malformations, intrauterine growth restriction, preeclampsia, and the need for cesarean delivery.

Ideally, weight loss should begin before pregnancy, first by trying lifestyle modifications (eg, increased exercise, dietary changes). Women who were overweight or obese are encouraged to limit weight gain during pregnancy to < 11.5 kg, ideally by modifying their lifestyle.

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

Exposure to Mercury

Mercury in seafood can be toxic to the fetus. The FDA (see Fish: What Pregnant Women and Parents Should Know ) recommends the following:

  • Avoiding tilefish from the Gulf of Mexico, shark, swordfish, and king mackerel

  • Limiting albacore tuna to 6 oz (one average meal)/wk

  • Before eating fish caught in local lakes, rivers, and coastal areas, checking local advisories about the safety of such fish and, if levels of mercury are not known to be low, limiting consumption to 6 oz/wk while avoiding other high-mercury seafood

Experts recommend that women who are pregnant or breastfeeding (and young children) eat 8 to 12 oz (2 or 3 average meals)/wk of a variety of seafood that is lower in mercury. Such seafood includes flounder, shrimp, canned light tuna, salmon, pollock, tilapia, cod, and catfish. Fish has nutrients that are important for fetal growth and development.

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 Table: 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. 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 a 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

  • 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 or oligohydramnios is 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 the following:

  • Fetal growth restriction

  • Preterm labor

  • Abruptio placentae

  • Congenital malformations

  • Perinatal morbidity and mortality

  • After delivery, uterine atony and hemorrhage

Multifetal pregnancy is detected during routine ultrasonography at 16 to 20 wk.

Prior Birth Injury

Most cerebral palsy and neurodevelopmental disorders are 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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