Chapter 89 High-Risk Pregnancies

High-risk pregnancies are those that increase the likelihood of abortion, fetal death, premature delivery, intrauterine growth restriction, poor cardiopulmonary or metabolic transitioning at birth, fetal or neonatal disease, congenital malformations, mental retardation, or other handicaps (see Table 89-1 on the Nelson Textbook of Pediatrics website at www.expertconsult.com ; Chapter 90). Some factors, such as ingestion of a teratogenic drug in the 1st trimester, are causally related to the risk; others, such as hydramnios, are associations that alert a physician to determine the etiology and avoid the inherent risks associated with excessive amniotic fluid. On the basis of their history, 10-20% of pregnant women can be identified as being at high risk; nearly half of all perinatal mortality and morbidity is associated with these high-risk pregnancies. Although assessing antepartum risk is important in reducing perinatal mortality and morbidity, some pregnancies become high risk only during labor and delivery; therefore, careful monitoring is critical throughout the intrapartum course.

Identifying high-risk pregnancies is important not only because it is the 1st step toward prevention but also because therapeutic steps may often be taken to reduce the risks to the fetus or neonate if the physician knows of the potential for difficulty.

Maternal Factors

The lowest neonatal mortality rate occurs in infants of mothers who receive adequate prenatal care and who are 20-30 yr of age. Pregnancies in both teenagers and women older than 40 yr, particularly primiparous women, are at increased risk for intrauterine growth restriction, fetal distress, and intrauterine death. Advanced maternal age increases the risk of both chromosomal and nonchromosomal fetal malformations (Fig. 89-1).

Figure 89-1 Natural birth prevalence of Down syndrome according to maternal age.

(From Wald NJ, Leck I: Antenatal and neonatal screening, ed 2, Oxford, 2000, Oxford University Press.)

Maternal illness (Table 89-2), multiple pregnancies (particularly those involving monochorionic twinning), infections (Table 89-3), and certain drugs (Chapter 90) increase the risk for the fetus. The use of assisted reproductive technology (in vitro fertilization, intracytoplasmic sperm injection) increases the risk of perinatal mortality, infant morbidity, prematurity, low and very low birthweight, and cerebral palsy, largely because of the increase in multiple-fetus pregnancies with such technology; the risks for birth defects are also increased, in part, because of epigenetic effects on gene expression.

Table 89-2 MATERNAL CONDITIONS AFFECTING THE FETUS OR NEONATE

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DISORDER	EFFECT(S)	MECHANISM(S)
Autoantibody against folate receptors	Neural tube defects	Blockage of cellular uptake of folate
Cervical neoplasia	Preterm premature rupture of membranes	Associated with loop electrosurgical excision procedure or cone therapy
Cholestasis	Preterm delivery, intrauterine fetal demise	Unknown, possibly hepatitis E
Cyanotic heart disease	Intrauterine growth restriction	Low fetal oxygen delivery
Diabetes mellitus:
Mild	Large for gestational age, hypoglycemia	Fetal hyperglycemia—produces hyperinsulinemia; insulin promotes growth
Severe	Growth restriction	Vascular disease, placental insufficiency
Drug addiction	Intrauterine growth restriction, neonatal withdrawal	Direct drug effect plus poor diet
Endemic goiter	Hypothyroidism	Iodine deficiency
Graves disease	Transient neonatal thyrotoxicosis	Placental immunoglobulin passage of thyroid-stimulating antibody
Herpes gestationis (noninfectious)	Bullous rash, intrauterine fetal demise	Unknown
Hyperparathyroidism	Neonatal hypocalcemia	Maternal calcium crosses to fetus and suppresses fetal parathyroid gland
Hypertension	Intrauterine growth restriction, intrauterine fetal demise	Placental insufficiency, fetal hypoxia
Idiopathic thrombocytopenic purpura	Thrombocytopenia	Nonspecific maternal platelet antibodies cross placenta
Isoimmune neutropenia or thrombocytopenia	Neutropenia or thrombocytopenia	Specific antifetus neutrophil or platelet antibody crosses placenta after sensitization of mother
Malignant melanoma	Placental or fetal tumor	Metastasis
Myasthenia gravis	Transient neonatal myasthenia	Immunoglobulin to acetylcholine receptor crosses placenta
Myotonic dystrophy	Neonatal myotonic dystrophy, congenital contractures, respiratory insufficiency	Genetic anticipation
Obesity	Macrosomia, hypoglycemia	Unknown
Phenylketonuria	Microcephaly, retardation	Elevated fetal phenylalanine values
Poor nutrition

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