Premature infants are those born before 37 weeks' gestation. Prevalence: ~6% singletons, 46% of twin, 79% of triplet or higher order deliveries. About 2% are before 32 weeks when neonatal problems are greatest. In 25%, delivery is elective (p 62). 10% are due to multiple pregnancy; 25% are due to APH, cervical incompetence, amnionitis, uterine abnormalities, diabetes, polyhydramnios, pyelonephritis, or other infections. In 40% the cause is unknown, but abnormal genital tract colonization (bacterial vaginosis) with ureaplasma and Mycoplasma hominis is implicated, either as a risk factor or risk marker. We also know that consumption of fish oil in pregnancy can ‘birth weight by “risk of recurrence of preterm delivery.1
Managing preterm rupture of membranes (PROM)
Admit; do T° MSU, and HVS using a sterile bivalve speculum. Assess for causes/associations: eg abruption, twins, and polyhydramnios. If liquor is not obvious its presence is suggested if nitrazine sticks (pH-sensitive) turn black (false +ve with infected vaginal discharge, semen, blood, and urine). In 80%, membrane rupture initiates labour. The problem with the 20% who do not go into labour is balancing advantages of remaining in utero (maturity and surfactant‘) against the threat of infection (causes 20% of neonatal deaths after PROM). Intrauterine infection supervenes after membranes have ruptured in 10% by 48h, 26% by 72h, 40% by >72h. Prophylactic antibiotics may allow labour to be delayed. If infection develops, do blood culture and give IV antibiotics (eg ampicillin 500mg/6h IV + netilmicin 150mg/12h IV) and expedite labour (p 62). Antibiotics for ~24h pre-labour, “rates of intraventricular haemorrhage and periventricular malacia (below) in the baby. If labour supervenes, allow it to progress. If liquor stops draining for >48h (rare) slowly mobilize the mother.42
Management of preterm labour
In 50% contractions cease spontaneously. Treating the cause (eg pyelonephritis) may make it cease. Attempts to suppress contractions (tocolysis) are unlikely to succeed if membranes are ruptured or the cervix >4cm dilated. The rationale for tocolytic use was that delay of preterm labour would improve fetal outcome without causing harm to mother or fetus. Trials have shown them to be of almost no clinical benefit, and only nifedipine is associated with improvement of fetal outcome. It is quite reasonable not to use tocolytic drugs; though they may be considered desirable in certain circumstances eg to give time for corticosteroids to work; or for in utero transfer.2 Use only between 24"33 weeks. Consider transfer to hospital with SCBU facilities. Call paediatrician to attend to the baby at birth. See cord-cutting recommendations p 58.
Tocolytic drugs
Absolute CI: chorioamnionitis, fetal death or lethal abnormality, condition (fetal or maternal) needing immediate delivery. Relative CI: fetal growth restriction or distress, pre-eclampsia, placenta praevia, abruption, cervix >4cm. β-sympathomimetics, associated with maternal fluid overload and pulmonary oedema are not recommended. Atosiban (licensed in Europe) has less maternal effects, has not been shown to benefit the fetus, and is expensive. Nifedipine is as effective, and associated with less newborn respiratory distress and admission to intensive care. Regimen: nifedipine 20mg PO then 10"20mg/6"8h PO according to uterine activity (unlicensed indication). SE: “BP; headache; flushing; pulse‘ (transient); myocardial infarction (very rare).43
1
S Olsen 2002 BMJ i447 If fish oil intake is low, small amounts of n-3 fatty acids provided as fish or fish oil may protect against prematurity & low birth weight.
2
K Groom 2004 The Obstetrician and Gynaecologist 6 41
Glucocorticoids
Betametasone 12mg IM followed by a second dose 12 hours later, (or, less favoured dexamethasone 6mg/12h × 4 doses) promote fetal surfactant production, lowering mortality and complications of RDS (p 118) by 40"50%. They also help close patent ductuses and protect against periventricular malacia, a cause of cerebral palsy. Use between 24 and 34 weeks. Avoid if maternal systemic infection eg TB.
If diabetic, monitor glucose. Benefit is maximal after 24h; effects last a week.
Prematurity, survival, and disability the figures
ne major, landmark question is: Is the baby over 28 weeks' gestation?
- The disability rate is 25% if gestation is <28 weeks but half this if gestation is 28"29 weeks.
- 10% of those who survive at gestations <28 weeks will never be independently mobile, or communicate intelligibly with others.
- Only 4% of babies born before 24 weeks will survive, and of survivors, >50% will be severely disabled.
- Use of surfactant (p 118) has not reduced the viability threshold, or rates of severe disability in babies born at <28 weeks' gestation.
- Of babies born >30 weeks' gestation, in the absence of deformity, ~100% now survive.
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