4
Prepregnancy care, prenatal screening and fetal medicine

Prepregnancy care

To optimize the chances of a healthy baby, mothers are advised:

Attend clinic for prenatal care.
Avoid or cease maternal smoking, alcohol, drug misuse,medication (unless essential) prior to conception.
Toxoplasmosis exposure – avoid eating undercooked meat (and wear gloves when handling cat litter).
Listeria infection – avoid unpasteurized dairy products and soft ripened cheeses, e.g. brie.
Folic acid supplements preconceptually to 12 weeks – to reduce risk of neural tube defects and cardiac malformations in countries without folic acid fortification of foods, as in the UK and Europe. Higher dose if previous baby with neural tube defect.
Avoid eating shark, swordfish, marlin and limit tuna as high levels of mercury. Limit oily fish as contain pollutants.
Optimize management of pre–existing maternal medical conditions such as diabetes and hypertension.

Pregnancies at increased risk of fetal abnormality need to beidentified:

previous child with congenital anomaly
family history of an inherited disorder, consanguineous
parents known carriers of an autosomal recessive disorder
parents from ethnic group with specific risk, e.g. Ashkenazi Jews (Tay–Sachs disease, a neurodegenerativedisorder)
parent with known balanced chromosomal rearrangement.

Prenatal screening

Maternal blood

The routine screening tests vary geographically, but include:

maternal blood group, antibodies against rhesus (D) and other red cell incompatibilities
hepatitis B (surface and e-antigen status)
syphilis serology,
rubella,
HIV infection
screening for chromosomal anomalies (see below)
hemoglobin electrophoresis.

Ultrasound

Ultrasound screening is recommended for all mothers before 20 weeks. Usually involves two ultrasound scans:

a late first-trimester scan (11 weeks to 13 weeks 6 days)
a mid-trimester scan (18 to 22 weeks).

Ultrasound screening allows:

Gestational age calculation, optimal at late first trimester scan.
Multiple pregnancy to be identified – number of fetuses and the chorionicity (number of placentae and amniotic sacs).
Structural malformations – up to 80% of major congenital malformations can be identified.
Screening for trisomy 21 (Down syndrome). First trimester – nuchal translucency measurement combined with serum maternal hormones. Second trimester – four fetoplacental and maternal hormones in serum, adjusted for maternal age. Confirmed on amniocentesis or chorionic villous sampling. Detects about 90% with trisomy 21, but 3–5% false positive rate and 1% risk of fetal loss.
Non-invasive prenatal testing (NIPT) – fetal DNA from maternal blood for trisomies, Rhesus, gender.
Fetal growth monitoring – by serial measurement of fetal head size (biparietal diameter and head circumference), abdominal circumference and femur length.
Amniotic fluid volume assessment to identify:
1. oligohydramnios – may result in pulmonary hypoplasia and limb and facial deformities
2. polyhydramnios – associated with maternal diabetes, fetal bowel obstruction, CNS anomalies and multiple births.
Doppler ultrasound measurement of flow/velocity waveforms – maternal and fetal circulation (if indicated).

Screening – Group B streptococcal, chlamydia, cystic fibrosis

In US but not UK. If at high risk of cystic fibrosis, a panel of common gene mutations is used.

Examples of structural malformations identified on ultrasound (Figs 4.1–4.3) (see videos: Fetal echocardiogram 1, Fetal echocardiogram 2, Fetal myelomeningocele)

c4-fig-0001 — **Fig. 4.1** Increased nuchal translucency associated with trisomy 21 (Down syndrome).

c4-fig-0002 — **Fig. 4.2** Sacral myelocele.

(Courtesy of Dr Venkhat Rahman.)

Fetal medicine

Fetal medicine (Fig. 4.4) may allow:

identification of congenital abnormalities (structural and chromosomal) with varying specificity and sensitivity of detection.
therapy (either indirectly or directly) to be given for a limited but increasing number of conditions, (e.g. fetal arrhythmias, intrauterine blood transfusion for severe rhesus disease)
optimal multidisciplinary discussion to impart information on prognosis and allow parents to make informed decisions including option of termination of pregnancy for severe disorders
optimal obstetric management of the fetus, e.g. timing of delivery
neonatal management to be planned in advance, e.g. counseling and transfer to specialty center.

c4-fig-0004 — **Fig. 4.4** Techniques in fetal medicine and their indications.

Fetal surgery

Creates media headlines as cutting-edge technology. However, the results are generally poor as the malformations justifying fetal surgery are severe, and the risk of premature labor is high. Now practiced only in a few centers and mainly restricted to randomized trials. Cases must be carefully selected.

Open fetal surgery

Randomized trial (MOMS) for myelomeningocele showed fetal surgery after hysterotomy (uterus opened at 19–25 weeks’ gestation) reduced the need for shunting and improved motor outcomes at 30 months. But uterine scarring and increased risk of preterm births.

Fetoscopic/minimally invasive fetal surgery

Fetal endoscopic tracheal occlusion (FETO) for congenital diaphragmatic hernia. As fetal tracheal obstruction promotes lung growth, this is replicated by inflating a balloon in the trachea, inserted at fetoscopy. Randomized controlled trial (TOTAL) shows slightly improved lung function in infancy though increased rate of preterm delivery and survival not improved (see Chapter 38).

Catheter shunts

For fetal pleural effusions, usually a chylothorax (lymphatic fluid) – inserted under ultrasound guidance (Fig. 4.5). Reduces risks of fetal death from hydrops and pulmonary hypoplasia. Neonatal course often satisfactory.
Congenital bladder neck obstruction – vesicoamniotic shunting. Controversial. A randomized controlled trial (PLUTO) showed shunt improved perinatal survival but did not reduce morbidity from renal disease or death at 2 years.

Fig. 4.5 Fetus with pigtail catheter to drain a pleural effusion.