“the woman's genes favor earlier onset of labor to expel the child, for her own survival, while those of the unborn child favor extension of the pregnancy to gain weight. So, they reach a kind of compromise deal”
15 of the gestational duration genetic variants act through the maternal genome
7 act both through the maternal and fetal genomes
2 act only via the fetal genome
initial assessment and Mx
aims
Ensure that the expected date of delivery is correct by reviewing early ultrasound scans
Assess for presence of risk factors and associations with preterm labour
Assess the likelihood of delivery within the next 7 days
assess frequency and regularity of uterine contractions
abdominal palpation to determine fetal size and presentation, assess for signs of chorioamnionitis, abruption etc.
if > 25+6 wks, contact midwife to perform CTG
contact obstetric registrar who may consider VE to:
Exclude PPROM
Visualise pooling of liquor (note presence of vernix)
Collect cervical and vaginal/anal (including GBS) microbiological swabs
Perform fetal fibronectin (fFN) testing where indicated (fFN is a screening test used to assess the risk of preterm delivery within the next seven days)
indications for fFN testing:
symptomatic preterm labour between 24 and 36 weeks gestation and intact membranes and cervical dilatation less than 3 cm
contra-indications to fFN testing:
Ruptured membranes
Visual evidence of moderate or gross bleeding (small amounts of bleeding do not appear to interfere).
Cervical cerclage insitu
relative C/I include:
After the use of lubricants or disinfectants
Within 24 hours of coitus
Within 24 hours of vaginal examination
In the presence of moderate or worse bleeding
Recent transvaginal scan
If PPROM excluded a digital assessment of cervical dilatation is appropriate (after fFN testing if indicated)
If >/= 3cm dilated or short cervix preterm labour likely.
consider USS:
to assess fetal number, size, presentation, fetal malformations (if morphology unknown), liquor volume and placenta localization, Doppler studies
if fFN is positive, consider requesting transvaginal ultrasound of cervical length (TVCL) as an additional screening test that can aid in assessing the risk of preterm delivery.
Mx of preterm labour
differentiating threatened preterm labour from preterm labour can be difficult and will often require repeated assessment (2 -4 hourly) for cervical change over time.
patients at low risk could be discharged home with review in 7 days, although those who have regular and painful contractions but none of the above features should be observed for 2 or more hours to assess whether or not it is only threatened rather than actual labour.
higher risk patients require admission or transfer and thus proceed with the following Mx if either:
positive fFN
evidence of cervical change (+/- TVCL < 15 mm)
contractions are persistent and painful
outcomes for extremely preterm infants depend on place of birth and access to neonatal intensive care.
Maternal transfer is generally safer for gestations < 32 weeks than neonatal retrieval if delivery is not imminent.
monitor
CTG monitoring until contractions cease
Pulse rate, respiratory rate and blood pressure monitoring
every thirty minutes for first hour, then
second hourly for 24 hours, then
four hourly
Measure and record temperature every four hours
prophylactic antibiotics
prophylactic antibiotics are not recommended in threatened preterm labour.
Prophylactic antibiotics for GBS should be administered in established preterm labour irrespective of GBS status.
iv benzyl penicillin 1.2g stat then 600mg 4hrly
Western Health policy 2013 advises Lincomycin 600 mg IV every 8 hours until delivery for those with penicillin hypersensitivity
The aim of tocolysis is to suppress uterine contractions and delay preterm delivery to:
allow in-utero transfer to an appropriate level facility, if appropriate,
allow for the administration of corticosteroids.
use immediate release tablets not sustained release tablets
initial dosing:
20mg orally stat
If contractions persist after 30 minutes: Repeat 20 mg
If contractions persist after a further 30 minutes: Repeat 20 mg
maintenance dosing:
If blood pressure is stable, 20 mg every 6 hours for 48 hours.
Further maintenance therapy is ineffective and is not recommended
Maximum dose is 160 mg/day
contraindications
Gestation > 34+0 weeks
Labour is too advanced
In-utero fetal death
Lethal fetal anomalies
Suspected fetal compromise
Placental abruption
Suspected intra-uterine infection
Maternal hypotension: BP < 90 mmHg systolic
relative contraindications
Cautiously give tocolysis if:
pre-eclampsia
placenta praevia (if not bleeding)
Nifedipine
Nifedipine is the tocolytic of choice ((King et al. 2003).
Nifedipine is a calcium channel blocker that relaxes smooth muscle.
It is an effective tocolytic with fewer side effects than other tocolytics available.
contraindications
previous adverse reaction to calcium channel blockers
maternal cardiac disease
hypotension
hepatic dysfunction
concurrent use with salbutamol or other beta-sympathomimetics
concurrent use of nitrates or antihypertensive medication
corticosteroids
corticosteroids are effective in reducing adverse perinatal outcomes, most notably respiratory distress syndrome, and in increasing the likelihood of neonatal survival (Roberts, Dalziel 2008)
initial dosing:
Administer IM betamethasone in two doses of 11.4 mg (5.7 mg x 2) 24 hours apart to the woman if birth is likely to occur between 23+0 and 35+0 weeks (N.B. The most recent RCOG guideline has increased the recommended threshold to 35+0 weeks). Monitor blood glucose levels, especially in women with diabetes.
maintenance dosing:
repeat doses of corticosteroids in pregnancy, either prophylactically or in the acute setting, should only be undertaken after consultant review. The use of repeat courses of steroids is best limited to gestation less than 32+0 weeks, in which case most women will have been transferred to a tertiary centre.
mode of delivery
less than 26+0 weeks
Cephalic presentation - Vaginal birth
Breech presentation – If aggressive neonatal management anticipated then caesarean section may be the safest mode of delivery if time permits. If the baby is at borderline gestation then vaginal birth may be more appropriate.
Multiple pregnancy – Caesarean section
26+0 weeks or greater
Cephalic presentation - vaginal birth
Breech presentation - caesarean section
care of the newborn
attendance of a paediatrician at the time of birth is essential
cord blood samples (arterial and venous) should be collected for blood gas analysis
collect and send placenta for:
histopathology (including check for chorioamnionitis)
swabbing for microbiological evidence of infection