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Risk Factors for Complications During Pregnancy


Raul Artal-Mittelmark

, MD, Saint Louis University School of Medicine

Last full review/revision Sep 2020| Content last modified Sep 2020
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Risk factors for complications during pregnancy include


Hypertensive disorders are classified as

  • Chronic hypertension: Present before the pregnancy or developing before 20 weeks of pregnancy

  • Gestational hypertension: New onset of high systolic and/or diastolic blood pressure (BP) > 140/> 90 mm Hg with no proteinuria and no signs of preeclampsia

  • Preeclampsia: New-onset hypertension (BP > 140/90 mm Hg) plus new unexplained proteinuria (> 300 mg/24 hours or urine protein/creatinine ratio ≥ 0.3) after 20 weeks or other signs of end-organ damage (eg, thrombocytopenia [platelets < 100,000/mcL], impaired liver function, renal insufficiency, pulmonary edema, or cerebral or visual symptoms).

  • Chronic hypertension plus superimposed preeclampsia: New or worsening proteinuria or other signs of end-organ damage after 20 weeks in a woman with preexisting hypertension

  • Severe preeclampsia or HELLP syndrome (hemolysis, elevated liver enzymes, and low platelet count)

Chronic hypertension is differentiated from gestational hypertension, which develops after 20 weeks of pregnancy. In either case, hypertension is defined as systolic BP > 140 mm Hg or diastolic BP > 90 mm Hg on 2 occasions > 24 hours apart.

Hypertension increases risk of the following:

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. Management of hypertension during pregnancy includes measurements of baseline renal function (eg, serum creatinine, blood urea nitrogen [BUN]), funduscopic examination, and directed cardiovascular evaluation (auscultation and sometimes ECG, echocardiography, or both). Each trimester, 24-hour urine protein, serum uric acid, serum creatinine, and hematocrit are measured. Ultrasonography to monitor fetal growth is done at 28 weeks and every 4 weeks thereafter. Delayed growth is evaluated with multivessel Doppler testing by a maternal-fetal medicine specialist. If women are at high risk of preeclampsia, clinicians should prescribe low-dose aspirin (81 mg orally once a day) to be taken daily starting at 12 to 28 weeks of gestation and taken until delivery (1).

Women with a history of preeclampsia or gestational hypertension are at a higher lifetime risk of cardiovascular events and, after delivery, should be referred for appropriate cardiovascular risk assessment and follow-up.

Hypertension reference

  • 1. ACOG Committee Opinion No. 743: Low-dose aspirin use during pregnancy. Obstet Gynecol 132 (1):e44–e52, 2018. doi: 10.1097/AOG.0000000000002708.


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:

The incidence of fetal macrosomia is about 50% higher in pregnant women with preexisting diabetes than in pregnant women in the general population. The incidence of perinatal mortality is also higher.

Women with preexisting diabetes are more likely to require preterm delivery for obstetric or medical indications. Exercise during pregnancy (with judicious changes in diet) reduces the need for cesarean and operative deliveries in these women (1, 2).

Tight glucose control before conception is essential to prevent fetal malformations.

Insulin requirements usually increase during pregnancy.

Gestational diabetes increases the risk of the following:

Gestational diabetes is routinely screened for at 24 to 28 weeks 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/m2

  • Certain ethnicities (eg, Mexican Americans, American Indians, Asians, Pacific Islanders) in whom diabetes is prevalent

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 Glucose Thresholds for Gestational Diabetes Mellitus Using a 3-hour Oral Glucose Tolerance Test). Based on a recommendation from the 2013 National Institutes of Health (NIH) consensus development conference, screening begins with a 1-hour 50-g glucose load test (GLT); if results are positive (plasma glucose > 130 to 140 mg/dL [7.2 to 7.8 mmol/L]), a 3-hour 100-g OGTT is done.


Glucose Thresholds for Gestational Diabetes Using a 3-hour Oral Glucose Tolerance Test*


Fasting mg/dL (mmol/L)

1-hour mg/dL (mmol/L)

2-hour mg/dL (mmol/L)

3-hour mg/dL (mmol/L)

Carpenter and Coustan

95 (5.3)

180 (10)

155 (8.6)

140 (7.8)

National Diabetes Data Group

105 (5.8)

190 (10.5)

165 (9.1)

145 (8)

* A 100-g glucose load is used.

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. Women with gestational diabetes are at a higher lifetime risk of cardiovascular events and, after delivery, should be referred for appropriate cardiovascular risk assessment and follow-up.


Threshold Values for Diagnosing Overt Diabetes in Pregnancy


Threshold Value

Fasting plasma glucose

126 mg/dL [7.0 mmol/L]



Random plasma glucose

200 mg/dL on > 1 occasion

* Fasting plasma glucose and HbA1C 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).

HbA1C = glycosylated hemoglobin.

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

Diabetes references

  • 1. Artal R: Exercise: The alternative therapeutic intervention for gestational diabetes. Clinical Obstetrics and Gynecology 46 (2):479–487, 2003.

  • 2. Artal R: The role of exercise in reducing the risks of gestational diabetes mellitus in obese women. Best Pract Res Clin Obstet Gynaecol 29 (1):123–4132, 2015.

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 hours of birth to minimize risk of transmission intrapartum.

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 HIV infection, hepatitis B, and syphilis and, if < 25 years, for chlamydial infection and gonorrhea 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.

Zidovudine or nevirapine is given to pregnant women with HIV infection. This treatmentreduces risk of HIV transmission to the fetus by two thirds; risk is probably lower (< 2%) with a combination of 2 or 3 antivirals. These drugs are recommended despite potential toxic effects in the fetus and woman.


During pregnancy, recurrent bacteriuria occurs more frequently, and the incidence of pyelonephritis is higher. If bacteruria is present, 20 to 35 % of pregnant women develop a urinary tract infection (UTI), and pyelonephritis is possible.

Pyelonephritis increases risk of the following:

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 hours 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:

However, surgery is usually tolerated well by pregnant women and the fetus when appropriate supportive care and anesthesia (maintaining blood pressure 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 hours.

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:

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. The risk of cervical insufficiency is higher in women who have had lacerations or injury of the cervix during a previous procedure (eg, therapeutic abortion, instrumental vaginal deliveries). Cervical insufficiency can be treated with surgical intervention (cerclage), vaginal progesterone, or sometimes a vaginal pessary.

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

Adolescents, 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 adolescents 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, chronic hypertension, diabetes). Because risk of fetal chromosomal abnormalities increases as maternal age increases, genetic testing should be offered.

Maternal Weight

Pregnant women whose body mass index (BMI) was < 19.8 kg/m2 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/m2 (overweight) or ≥ 30 kg/m2 (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 physical activity, dietary changes). Women who are overweight or obese are encouraged to limit weight gain during pregnancy, ideally by modifying their lifestyle. The Institute of Medicine (IOM) uses the following guidelines:

  • Overweight: Weight gain limited to < 6.8 to 11.3 kg (< 15 to 25 lb)

  • Obese: Weight gain limited to < 5 to 9.1 kg (< 11 to 20 lb)

However, not all experts agree with IOM recommendations. Many experts recommend an individualized approach that can include more limited weight gain plus lifestyle modifications (eg, increased physical activity, dietary changes), particularly for obese women (1). During pregnancy, most women should be encouraged to exercise at least 3 times a week for a total of 150 minutes each week (2).

For overweight and obese pregnant women, lifestyle modifications during pregnancy reduce the risk of gestational diabetes and preeclampsia.

Discussing appropriate weight gain, diet, and exercise at the initial visit and periodically throughout the pregnancy is important. The 2016 ACOG (American College of Obstetricians and Gynecologists) obesity toolkit is a helpful resource for managing overweight and obesity.

Maternal weight references

  • 1. Artal R, Lockwood CJ, Brown HL: Weight gain recommendations in pregnancy and the obesity epidemic. Obstet Gynecol 115 (1):152–155, 2010. doi: 10.1097/AOG.0b013e3181c51908

  • 2. Mottola MF, Davenport MH, Ruchat SM, et al: 2019 Canadian guideline for physical activity throughout pregnancy. Br J Sports Med 52 (21):1339–1346, 2018. doi: 10.1136/bjsports-2018-100056

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 week after conception (the 4th to 10th week 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

Commonly used drugs that may be teratogenic include

Hyperthermia or exposure to temperatures > 39° C (eg, in a sauna) during the 1st trimester has been associated with spina bifida.

Exposure to Mercury

Mercury in seafood can be toxic to the fetus. The FDA (see Advice About Eating Fish: For Women Who Are or Might Become Pregnant, Breastfeeding Mothers, and Young Children) recommends the following:

  • Avoiding tilefish from the Gulf of Mexico, shark, swordfish, big-eye tuna, marlin, orange roughy, and king mackerel

  • Limiting albacore tuna to 4 ounces (one average meal)/week

  • 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 4 ounces/week while avoiding other seafood that week

Experts recommend that women who are pregnant or breastfeeding eat 8 to 12 ounces (2 or 3 average meals)/week 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 weeks 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 weeks) 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, chronic hypertension, diabetes, infections) may lower risk of stillbirth in a current pregnancy.

Prior Preterm Delivery

Preterm delivery is delivery before 37 weeks. 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-week intervals after 20 weeks. Monitoring includes

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

  • 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 alpha-hydroxyprogesterone 250 mg IM once a week.

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). 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:

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

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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