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This is a plain English summary of an original research article. The views expressed are those of the author(s) and reviewer(s) at the time of publication.

If pregnant women develop late pre-eclampsia, after 34 but before 37 weeks of gestation, then planning to deliver their babies within 48 hours of the diagnosis reduces the risk of problems to the mother. This is compared with waiting until 37 weeks or delivering earlier if other problems arise (“expectant management”). However, this benefit needs to be offset against an increased likelihood of the baby being admitted to the neonatal unit.

This trial found that in women with late preterm pre-eclampsia, planned delivery reduces the chance of complications such as hypertension for the mother (65% versus 75% in the expectant management group). While their babies are more likely (42% versus 34%) to be admitted to the neonatal unit, there was not a significantly greater risk of morbidity.

The results of this study of 900 women will aid the decision-making process for women with late pre-eclampsia and the healthcare professionals involved in their care.

Why was this study needed?

Mild pre-eclampsia affects up to 6% of pregnancies, with severe cases developing in about 1 to 2% of pregnancies. Early signs include high blood pressure and having protein in the urine. Symptoms such as ankle swelling and headaches can occur if the condition progresses. In rare cases, there can be serious complications such as convulsions and stroke as well as stillbirth.

The cause is not yet fully understood, but it is thought to be linked to problems with the placenta. Delivering the baby is the only cure. Less urgent cases are usually monitored with the intent of progressing the pregnancy as far as possible to avoid complications associated with prematurity in the baby. The aim of this study was to determine whether inducing delivery earlier reduces the chance of harm to the mother without harming the baby despite the baby being born before they are considered fully developed.

What did this study do?

The PHOENIX randomised controlled trial allocated 448 women to planned delivery and 451 women to expectant management (usual care). All had late pre-eclampsia.

The trial took place in 46 consultant-led maternity units across England and Wales. Those in the intervention group were scheduled for initiation of delivery within 48 hours of randomisation to enable preparations such as neonatal lung acceleration to take place. Delivery was by induction of labour unless a caesarean section was necessary. Expectant management involved delivery at 37 weeks or sooner as per NICE recommendations.

Longer-term results from this trial are still being collected. For example, it will be useful to know if those infants in the intervention group have a higher incidence of developmental delay.

What did it find?

  • Babies in the planned delivery arm were born on average five days earlier than controls, according to their gestational age.
  • The primary outcome for the baby was a combination of either death or neonatal unit admission. This was higher in the planned delivery group affecting 196 (42%) infants compared with 159 (34%) infants in the expectant management group (adjusted relative risk [aRR] 1.26, 95% confidence interval [CI] 1.08 to 1.47). However, admission was mainly attributed to prematurity, without excessive respiratory or other morbidity, intensity of care, or length of stay, and there were no deaths.
  • The primary maternal outcome was either a recorded high systolic blood pressure of at least 160 mmHg after randomisation or any of the fullPIERS model outcomes (Pre-eclampsia Integrated Estimate of RiSk). This includes specific outcomes such as death, stroke and acute renal failure. The incidence of any of these outcomes was lower in the planned delivery group, affecting 289 (65%) women compared with 338 (75%) women in the expectant management group (aRR 0.86, 95% CI 0.79 to 0.94).
  • Progression to severe pre-eclampsia was the main adverse outcome for both maternal groups, affecting 287 (64%) women in the planned delivery group compared with 334 (74%) women in the expectant management group (aRR 0.86, 95% CI 0.79 to 0.94). There were no strokes, low incidence of other complications and one death that was thought to be unrelated to the trial.
  • Total maternal and infant costs were lower in the planned delivery group compared with the expectant management group, with an adjusted cost saving of £1,478 (95% CI £2,354 to £605).

What does current guidance say on this issue?

Recent NICE guidance on the diagnosis and management of hypertension in pregnancy recommends that women diagnosed before 34 weeks should be monitored until they reach 37 weeks unless the condition worsens. Intravenous magnesium sulphate and a course of antenatal corticosteroids should be offered in line with the NICE guideline on preterm labour and birth.

The advice for women between 34 and 37 weeks is the same, but in addition, it states that if considering a planned birth, it is important to take into account the woman's and baby's condition. A course of antenatal corticosteroids should be considered, in line with the NICE guideline on preterm labour and birth. At 37 weeks and above birth should be initiated within 24 to 48 hours.

What are the implications?

The results of this trial suggest that early planned delivery for late pre-term pre-eclampsia is better for the mother and does no harm to the baby, though at the cost of more admissions to the neonatal unit. If, as the authors of the trial suggest, alternative care strategies such as transitional care to enable mother and child to stay together, then this disadvantage could be minimised. Further long-term results are awaited.

Citation and Funding

Chappell LC, Brocklehurst P, Green ME et al. Planned early delivery or expectant management for late preterm pre-eclampsia (PHOENIX): a randomised controlled trial. Lancet. 2019;394:1181-90.

This project was funded by the NIHR Health Technology Assessment Programme (project number 12/25/03).



NHS website. Pre-eclampsia. London: Department of Health and Social Care; updated 2018.

NICE. Hypertension in pregnancy: diagnosis and management. NG133. London: National Institute for Health and Care Excellence; 2019.

NICE. Preterm labour and birth. NG25. London: National Institute for Health and Care Excellence; updated 2019.

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