Older mothers may benefit from being induced on their due date

Thursday November 16 2017

"Inducing birth one to two weeks earlier in first-time mothers over 35 could reduce stillbirths by two-thirds, large study finds," reports the Mail Online.

In the UK, the practice in most cases is to wait until week 42 of pregnancy to see if labour begins naturally before offering to induce the pregnancy. Induction of labour involves putting into the vagina a hormone tablet or gel that softens the cervix and may stimulate contractions.

The researchers looked at data from 77,327 births involving mothers aged 35 or above in the UK, which showed that inducing birth at 40 weeks for this population lowered the risk of stillbirth by 75%. It also reduced the risk of perinatal deaths (stillbirths and deaths within the first week after birth) by 67%.

However, although the figures in the headlines sound major, they relate to very small numbers of cases: perinatal deaths occurred in 0.08% of women who were induced compared with 0.26% of women who were not.

We also don't know why some of the women needed to be induced. There are many possible reasons for having an induction, such as having pregnancy-related diabetes or high blood pressure. For mothers with these known complications, it's standard practice in the NHS to monitor them closely and offer earlier induction with balanced information on the benefits and risks.

Clinical guidelines are frequently revised and updated and, while a single study is unlikely to lead to a change, this evidence will come under consideration.

Where did the story come from?

The study was carried out by various UK institutions, including the London School of Hygiene & Tropical Medicine, the Royal College of Obstetrics and Gynaecologists, and the University of Cambridge. It was published in the peer-reviewed journal PLOS Medicine on an open-access basis, so it's free to read online. No sources of financial support were reported.

The media coverage had slightly different takes. BBC News reported the story fairly accurately, pointing out that inductions are offered to first-time mothers aged 35 or older because this group is "generally at a higher risk of birth complications".

The Mail Online, however, added an inaccurate point that offering earlier inductions across the board to older mothers would have an "enormous" effect on the cost to the NHS of giving birth. The study did not evaluate the cost impact at all. In fact, the authors recommended this as an area for future research.

Both reports failed to mention the limited generalisability of this research – it's more relevant to women aged 35 or older who already have a medical complication.

There were also issues with the data used, meaning some important information that could have affected the results was not recorded.

What kind of research was this?

This was a UK cohort study of expectant first-time mothers aged 35 or older.

This type of study is good for looking at links between factors, such as induction of labour and how this might influence the chance of a baby dying during or shortly after pregnancy. However, they cannot prove that one factor causes another.

A randomised controlled trial would be most appropriate to determine causation but, in the case of pregnant mothers, this would be complicated because stillbirths and perinatal deaths are quite rare. Also, if there was an expected benefit to having an early induction, then giving it to one group and not the other could be seen as unethical.

What did the research involve?

The researchers looked at first-time mothers aged 35 to 50 who were induced at 39, 40 or 41 weeks. They wanted to see if the time of induction made any difference to perinatal death rates in comparison with "watching and waiting" until week 42. Perinatal death was defined as stillbirth or in-hospital death of the baby within 7 days of birth.

The researchers examined "hospital episode statistics" (HES) gathered between April 2009 and March 2014. HES are made up of information routinely collected by hospital staff during a patient's general use of hospital services. This usually includes information such as how many hospital admissions people have had, the reasons for their admission and whether they had an adverse event while in hospital.

They identified 77,327 women, 25,583 (33.1%) of whom were induced and 51,744 (66.9%) of whom were not. The researchers excluded pregnant mothers who:

  • were due to give birth to multiple babies
  • had serious health conditions or risk factors before getting pregnant, such as high blood pressure, diabetes or lung disease
  • had an unborn baby with an abnormality
  • had birth complications, such as breech presentation
  • were induced because their baby died in the womb
  • were induced because their waters had broken but they had not gone into labour

In the analysis, the researchers adjusted as best they could for potential confounding factors such as:

  • mother's age
  • mother's ethnicity
  • mother's socio-economic status (a measure combining economic, social and housing indicators)
  • year of the baby's birth
  • sex of the baby
  • birthweight of the baby

What were the basic results?

Induction at week 39

Compared with no intervention (often called "expectant management"), induction at 39 weeks was associated with:

  • No difference in perinatal death or stillbirth.
  • Increased risk of low oxygen in the baby during labour (5.9% vs 7.73%; adjusted relative risk [aRR] 0.74, 95% confidence interval [CI] 0.65 to 0.85).
  • A 78% lower risk of meconium aspiration syndrome (0.16% vs 0.74%; aRR 0.22, 95% CI 0.10 to 0.49). This condition occurs when the first stool of the infant is released into the protective liquid surrounding the baby in the womb, which can cause breathing problems if inhaled by the baby.

Induction at week 40

Induction at 40 weeks was associated with:

  • A 67% lower risk of in-hospital perinatal death (0.08% vs 0.26%; aRR 0.33, 95% CI 0.13 to 0.80). This meant that 562 inductions of labour at 40 weeks would be required to prevent 1 perinatal death.
  • A 75% lower risk of stillbirth (0.05% vs 0.22%; aRR 0.25, 95% CI 0.08 to 0.79).
  • A 48% lower risk of meconium aspiration syndrome (0.44% vs 0.86%; aRR 0.52, 95% CI 0.35 to 0.78).
  • A 6% increased risk of deliveries requiring the assistance of a surgical instrument, such as forceps (27.88% vs 28%; aRR 1.06, 95% CI 1.01 to 1.11) or emergency caesarean section (38.94% vs 33.38%; aRR 1.05, 95% CI 1.01 to 1.09).

Induction at week 41

Induction at 41 weeks was associated with:

  • A 76% lower risk of in-hospital perinatal death (0.07% vs 0.30%; aRR 0.24, 95% CI 0.09 to 0.65).
  • An 82% lower risk of stillbirth (0.04% vs 0.24%; aRR 0.18, 95% CI 0.05 to 0.65).
  • A 43% lower risk of meconium aspiration syndrome (0.57% vs 0.99%; aRR 0.57, 95% CI 0.39 to 0.83).
  • A 6% lower risk of emergency caesarean section (41.27% vs 42%; aRR 0.94, 95% CI 0.90 to 0.97).

How did the researchers interpret the results?

The researchers stated that for women aged 35 years or older and expecting their first child: "Bringing forward the routine offer of induction of labour from the current recommendation of 41-42 weeks to [after] 40 weeks of gestation ... may reduce overall rates of perinatal death."

They added: "It is, however, important to note the potential downsides to a policy which would significantly increase the use of labour induction, and further studies should examine the impact of such a policy on resource utilisation and patient satisfaction."

Conclusion

This study provides some interesting and useful findings for pregnant mothers over the age of 35 who are expecting their first child.

Its strengths lie in the large cohort of women, which was made possible by taking advantage of hospital episode data over a 5-year period. This equipped the researchers with the ability to determine outcomes within the first week by following up newborns after they were discharged from hospital.

It's important to note that, although hospital episode statistics gather a lot of very useful health data, under-reporting is common and the information available can vary between hospitals. For example, in this study:

  • Gestational age was recorded in weeks rather than days, limiting the specificity of the results.
  • Ethnicity data was missing in 9% of cases.
  • Under-reporting of inductions was suspected.
  • The researchers were unable to adjust for the important possible confounder of maternal obesity.
  • Mothers who were induced were more likely to have had pregnancy complications such as pre-eclampsia (high blood pressure brought on by pregnancy), gestational diabetes (again brought on by pregnancy) and abnormal amniotic fluid volume (fluid around the baby), and the babies were also more likely to be lighter. This means they may not be representative of older mothers in general.

Furthermore, the observed number of perinatal deaths was comparatively small (0.3% overall), which means that any under-reporting in the hospital data would have a major effect on the results.

This study therefore does not provide strong evidence that an earlier induction than is currently recommended is beneficial for all expectant mothers.

Earlier induction may provide benefits for a specific group of older mothers, but mothers over 35 with other health conditions are likely to be closely monitored and offered an earlier induction anyway.

It's advisable to discuss any concerns or preferences you may have about being induced with your midwife and doctor.

Analysis by Bazian
Edited by NHS Choices