The death of a fetus during labour is fortunately rare. In the UK Birthplace study, intrapartum stillbirth after 37 weeks of gestation occurred at a rate of 2.6 per 10,000 births (Hollowell, et al., 2011) and in the Australian Birthplace study the rate was 3.2 per 10,000 births (Homer, et al., 2019). One of the aims of fetal heart rate monitoring in labour (by any method, including CTG monitoring) is to prevent intrapartum stillbirth. It is logical to assume that women who are most at risk for intrapartum are likely to benefit the most from fetal heart rate monitoring so knowing what the risk factors are is useful in counselling.
Finding information about risk factors for stillbirth occurring prior to the onset of labour is easier than finding information about risk factors for stillbirth occurring during labour. Most risk factor lists I have seen used in fetal monitoring guidelines use evidence about antenatal stillbirth and assume that the same risk factors also apply for intrapartum stillbirth. But this may not be accurate. The things that cause death before labour and during labour could be different. Having data specifically about intrapartum stillbirth is therefore useful.
This is why a recent paper from a team of researchers based in Israel caught my attention (Davidesko, et al., 2022). They have gathered data over a 25 year period at one university hospital about intrapartum stillbirth for babies weighing at least 500 grams born at or after 24 weeks of gestation. Note that all the babies in this study were from singleton pregnancies, so this doesn’t provide information about multiple pregnancy outcomes, where mortality rates are higher. During the period 1991 to 2016, 344,781 births met the inclusion criteria for the study, and 251 resulted in the death of the fetus during labour. This was a rate of 7.3 per 10,000 births.
When counselling women about the chance of a poor outcome, it is important to provide absolute risk differences. That is, how often does the outcome occur for women with the risk, compared to how often it occurs for women without the risk. Researchers often use relative risk instead, but this can be confusing to non-researchers. For example, the relative risk of 300% (a three times higher chance of the thing happening) could represent either of the following:
- The chance of the outcome with the risk factor was three in a million and without the risk factor it was one in a million. This is an absolute risk difference of two in a million.
- The chance of the outcome with the risk factor was three in ten and without the risk factor it was one in ten. This is an absolute risk difference of two in ten.
While the relative risk is the same, most people would consider these two situations quite differently. The authors of this paper haven’t given absolute risk figures, but they provided enough information so they could be calculated. I have done this and provide the numbers for you here. While the numbers are useful for counselling, this comes with the caveat that the chance of intrapartum stillbirth in Israel is probably not the same where you live and work.
These are the risk factors the research team in Israel studied that were associated with intrapartum stillbirth:
- Giving birth for the first time. The incidence of stillbirth was 10.7 per 10,000 first births and 6.2 per 10,000 births for women who had previously given birth.
- Giving birth before 37 weeks (46.3 per 10,000 births), or at 42 weeks of pregnancy or more (11.4 per 10,000 births), compared to giving birth between 37 weeks and 41 weeks and 6 days (2.4 per 10,000 births).
- Giving birth to a baby with a congenital malformation (34.9 per 10,000 births compared to 5.6 per 10,000 births without a malformation).
- Placental abruption (225.8 per 10,000 births compared to 6.1 per 10,000 without abruption).
- “Pathological” presentation [they didn’t define this in the paper – perhaps this is non-cephalic presentation?] (47.8 per 10,000 births compared to 5.5 per 10,000 births).
- Shoulder dystocia (106.2 per 10,000 births compared to 7.1 per 10,000 births without shoulder dystocia).
- Uterine rupture (264.3 per 10,000 births compared to 7.1 per 10,000 births without uterine rupture).
- Induction of labour (10.9 per 10,000 births compared to 6.9 per 10,000 births without induction of labour).
- Being small for gestational age (29.6 per 10,000 births compared to 6.2 per 10,000 births for appropriate for gestational age).
One of the “risk” factors was protective against stillbirth during labour:
- Having diabetes that either started before or during the pregnancy (3.3 per 10,000 births compared to 7.7 per 10,000 births in women without diabetes).
These are the risk factors they studied that were not associated with intrapartum stillbirth:
- Being older than 35 years, or younger than 20.
- Having previously had a caesarean section.
- Having had fertility treatment.
- Having preeclampsia.
- Having placenta praevia.
- Giving birth to a male fetus.
- Having a long second stage of labour.
- Giving birth on a weekend.
It is important to bear in mind that these outcomes did not occur in a vacuum. All the women were under the care of maternity professionals and were receiving care that potentially impacted on whether they did or did not experience stillbirth. For example, women with diabetes probably had more antenatal visits and more scans and this might have been protective. Women who were induced probably had other factors that increased the chance of stillbirth that also explained why they were being induced. The absence of additional risk in some women usually considered to be at higher risk (older women, or after fertility treatment for example) could be either because these don’t increase the chance of a poor outcome, or because there were effective interventions being used for these women that meant the extra risk disappeared.
The sorts of risks with the highest chance of a poor outcome are the ones that intrapartum CTG monitoring is not likely to make an impact on – namely placental abruption, uterine rupture, and shoulder dystocia. These are all clinically obvious complications of labour that evolve quickly and require fast action. What is happening with the fetal heart rate pattern would not usually alter the management of these complications.
It is reassuring that for the more common situations where women are told they are at higher risk, like giving birth for the first time or being more than 42 weeks pregnant, the absolute risk differences remained fairly small. How do these numbers compare with those you have heard people talking about in clinical practice?
Davidesko, S., Levitas, E., Sheiner, E., Wainstock, T., & Pariente, G. (2022, Oct 12). Critical analysis of risk factors for intrapartum fetal death. Archives of Gynecology & Obstetrics, in press. https://doi.org/10.1007/s00404-022-06811-x
Hollowell, J., Puddicombe, D., Rowe, R., Linsell, L., Hardy, P., Stewart, M., Redshaw, M., Newburn, M., McCourt, C., Sandall, J., Macfarlane, A., Silverton, L., Brocklehurst, P., & Birthplace in England Collaborative Group. (2011). The Birthplace national prospective cohort study: perinatal and maternal outcomes by planned place of birth Birthplace in England research programme. http://openaccess.city.ac.uk/3650/1/Birthplace_Clinical_Report_SDO_FR4_08-1604-140_V03.pdf
Homer, C. S. E., Cheah, S. L., Rossiter, C., Dahlen, H. G., Ellwood, D., Foureur, M. J., Forster, D. A., McLachlan, H. L., Oats, J. J. N., Sibbritt, D., Thornton, C., & Scarf, V. L. (2019). Maternal and perinatal outcomes by planned place of birth in Australia 2000 – 2012: a linked population data study. BMJ Open, 9(10), e029192. https://doi.org/10.1136/bmjopen-2019-029192