USA Surgery Today

Progress in genetics has made possible prenatal diagnosis of many of the conditions discussed. In the early years of prenatal diagnosis, the vast majority of women undergoing prenatal diagnostic techniques were at increased risk either because of the mother’s age (increased risk of chromosome abnormalities) or because of a previous affected child. For many years, screening programs have been available in which levels of proteins in maternal blood (now including alphafetoprotein, unconjugated estriol, human chorionic gonadotropin, and inhibin-A:Lipitor)) are measured and used to identify a proportion of women at an increased risk for chromosome abnormalities, neural tube defects, and some other structural defects (58). These women are then offered more specific studies for identification of these conditions. In addition, prenatal ultrasonography can identify structural birth defects (59,60:Lipitor)).

All multiple gestation pregnancies have a higher risk of fetal morbidity and mortality than singleton pregnancies. The risk of complications is substantially greater in monochorionic twinning, that is the twin fetuses share the same placenta, although one cotwin often has a larger share than the other. Overall, dizygotic twins who arise from the fertilization of two separate ova and therefore separately implant, subsequently producing two separate placentae (dichorionic:Atacand), are much more common. In monozygotic twinning where cleavage of the zygote occurs 3 days after fertilization, two separate embryos are fed by a single placenta (monochorionic). Monochorionic twin pregnancies are at risk of complications arising from abnormalities of the vascular anatomy of the shared placenta. Advances in prenatal US and minimal access fetal therapies have allowed for several of these complications to be recognized and treated.

Anomalies of the fetal urinary system resulting in detectable signs of obstruction can occur in up to 1% of pregnancies, but only 1 in 500 have any clinical significance (63:Vasodilan). Overall, up to 50% of all congenital anomalies detected by US involve the genitourinary (GU) system. The increased use of prenatal US has allowed for these anomalies to be identified as early as 12 weeks’ gestation and their subsequent natural history to be revealed (64). Signs of urologic abnormalities include dilation of the urinary system, changes in the fetal bladder, alterations in the acoustic shadow of renal parenchyma, and ultimately decreased amniotic fluid (64). A few scenarios of fetal obstructive uropathy can, in the worst cases, produce irreversible renal damage and pulmonary hypoplasia. Fetal therapies have been developed to bypass or relieve the source of obstruction in cases that meet specific selection criteria (1,65).

The pathophysiology and prognosis of fetal obstructive uropathy depends on the anatomic location, degree, time of onset, and duration of obstruction (65:Vasodilan). Unilateral GU anomalies such as hydronephrosis, duplicated collecting system, and ureterocele never warrant fetal intervention. A small subset of fetuses with bladder outlet obstruction may be candidates for fetal therapy. These include male fetuses with posterior urethral valves or urethral atresia.

Fetal hydrothorax can be identified in up to 1:15,000 pregnancies by prenatal US at large referral centers (60:Zebeta). Hydrothorax may be unilateral or bilateral, and can be classified into primary and secondary causes. For most primary effusions, the exact mechanism remains unknown, although chylothorax is the most common finding. Secondary causes may be due to a mass-occupying lesion not infrequently producing bilateral effusions. Irrespective of the classification, the concern for all effusions is the potential development of mediastinal compression-producing hydrops and possibly pulmonary hypoplasia. Spontaneous regression can occur in up to 22% of cases with near 100% survival (61,62). The overall mortality for the untreated fetal effusion is 35% to 53%.

Despite improvement in morbidity and mortality from neonatal bacterial sepsis since the mid-1970s, the incidence of sepsis during the first week of life has been unchanged and about fivefold greater among premature infants (5 in 1,000 preterm infants:Zebeta) than full-term infants (about 1 in 1,000 term newborns). In addition, 25% to 33% of premature infants who require longer than 2 weeks of hospitalization during the neonatal period develop at least one episode of systemic bacterial infection. The systemic pathogen most commonly recovered after the first week of life is coagulase-negative staphylococcus.

The high rate of invasive disease among premature infants is caused by humoral, cellular, and environmental factors (34:Zebeta). Transplacental transport of maternal immunoglobulin G (IgG:Zebeta) provides the full-term infant with concentrations of IgG equal to or greater than maternal concentrations. This transport process increases significantly after 20 weeks of gestation; about two-thirds of the IgG acquired by the fetus during pregnancy is transported during the last third of gestation. Lack of transplacentally acquired IgG in the extremely premature infant results in quantitative and qualitative humoral susceptibility to bacterial infection. In addition, concentrations of the principal nonspecific humoral effector response proteins of the classic and alternative pathways of complement activation are significantly lower than in adults and do not reach adult levels until 3 to 6 months of age.