When you become pregnant, the due date may be calculated in two ways – using the date of the first day of the most recent period, or by ultrasound. Both of these methods have limitations – someone may not know the date of their last period, and this method assumes a 28 day cycle. Ultrasound also has margin for error - the position of the fetus and body shape of the mother can affect accuracy. Around 66% of babies are born within one week either side of the calculated due date.
The usual length for a pregnancy, considered ‘normal’ – is 37-42 weeks. After 40 weeks a pregnancy is considered to be ‘post-dates’, and after 42 weeks ‘post-term’. In Australia, induction is offered when a pregnancy becomes post-dates, to prevent it becoming post-term. As a result, less than 1% of pregnancies continue beyond 42 weeks.
Due dates are important in terms of emotional and practical preparations for birth, and also for high risk pregnancies where interventions or planned caesareans are needed. However due dates can also become stressful time limits – for instance – if a birthing woman or person is hoping for an intervention-free birth, the pregnancy going ‘overdue’ or post-dates increases likelihood of pressure from hospital caregivers for induction and other, potentially unwanted, interventions.
What is induction?
Induction is where a woman or birthing person’s labor is deliberately started, rather than the labor starting spontaneously. Induction is used where there is a complication or variation to pregnancy. This could be something serious like pre-eclampsia, an illness that threatens both the birthing woman and baby, or going ‘overdue’ in the length of the pregnancy.
If induction is raised as a potential pathway for instigating labor, the health professional should explain the reasons for inducing, when and how it will occur, options for pain relief, risks and benefits of induction and alternative options if an induction is refused by the birthing woman or person. If your caregiver does not explain these things then ask, as you are the ultimate decision maker for your birth.
There are a few steps in the induction process. The first may be a membrane sweep, which is where a practitioner sweeps their finger around the inside of the lower part of the uterus – the aim being to separate the membranes of the amniotic sac from the lower uterus and to prompt the body to release its own prostaglandins, which may initiate contractions. This procedure can be physically uncomfortable.
If the cervix is firm and closed, artificial prostaglandins may be applied to the cervix in the form of a gel or pessary. This process may require a few applications of prostaglandins, so can take hours or even days. Sometimes a balloon catheter is inserted into the cervix to prompt natural prostaglandin release. Once labor is started the baby’s heart rate will be monitored with a CTG and this kind of induced labor will be considered ‘high risk’.
Once the cervix is softened, am amnihook is sued to artificially break the waters. The baby’s head will press harder on the cervix, facilitating more effective contractions. Once waters have been broken, you can wait for some hours to see if the labor begins, or proceed to artificial oxytocin. This is administered via a cannula and your baby will be monitored by a CTG. Artificially stimulated contractions are described as different and more painful by birthing women and people. The progression of the labor may happen more quickly and with more intensity, as the body is not able to slowly build up its natural response to pain. Once the baby is born, artificial oxytocin is required to birth the placenta.
Here is an article that describes the induction process in detail.
It is important to realise that once you consent to induction, you are consenting to some or all of the interventions just described. You will need to have an IV drip and constant monitoring, limiting your range of movement. Induction carries certain risks such as fetal distress and impact on the birthing woman or person, and increases the likelihood of requiring other interventions, such as an epidural and instrumental birth. There may be an increased risk of requiring a caesarean, especially if it is your first birth.
What the research says
In Australia, about one third of all birthing women and people are induced, with the most common reason being to avoid a ‘prolonged pregnancy’. Some of the concerns in relation to this include an ‘ageing placenta’, the baby growing too big, or increased risk of stillbirth. Research is mixed in terms of the concept of an ageing placenta - one study showed that placentas from stillborn babies did show oxidation commensurate with a late-term placenta (remember that overall rates of stillbirth are very low), while another study showed no evidence that post-term pregnancy increased any risk, and that no evidence that routine induction by 42 weeks’ gestation improved maternal or neonatal outcomes. For big babies, research shows that it is the interventions carried out because of an assumption of a big baby are the cause of complications, rather than the size of the baby.
One study found that risk of caesareans was more than doubled when elective induction was employed, and especially if cervical ripening agents are used. The 2021 BESt study, which asked women what they want for future births, reported that 5% of respondents said they would avoid induction in future births. If you are facing induction, be sure to ask lots of questions and do your own research in order to fully understand the risks and benefits. Think about what you will consent to in advance, and how long ‘overdue’ you are comfortable with.
Here and here are links to articles discussing the risks of induction in more detail.
References
Davey, M., & King, J. (2016). Caesarean section following induction of labour in uncomplicated first briths – a population-based cross-sectional analysis of 42950 births. BMC Pregnancy and Childbirth, 16(92). https://doi.org/10.1186/s12884-016-0869-0
Gu, V., Feeley, N., Gold, I., Hayton, B., Robins, S., Mackinnon, A., Samuel, S., Carter, C.S., & Zelkowitz, P. (2016). Intrapartum synthetic oxytocin and its effects on maternal well-being at 2 months postpartum. Birth, 43(1), 28-35. doi: 10.1111/birt.12198
Jonsson, M., Cnattingius, S., & Wikstrom, A. (2012). Elective induction of labor and the risk of caesarean section in low-risk parous women: A cohort study. Acta Obstetricia et Gynecologica Scandinavica, 92(2), 198-203. https://doi.org/10.1111/aogs.12043
Keedle, H., Lockwood, R., Keedle, W., Susic, D., & Dahlen, H.G. (2023). What women want if they were to have another baby: The Australian Birth Experience Study (BESt) cross-sectional national survey. BMJ Open, 13, e071582. doi:10.1136/ bmjopen-2023-071582
Maiti, K., Sultana, Z., Aitken, R.J., Morris, J., Park, F., Andrew, B., Riley, S.C., & Smith, R. (2017). Evidence that fetal death is associated with placental aging. American Journal of Obstetrics and Gynecology, 217(4), 441.e1. https://doi.org/10.1016/j.ajog.2017.06.015
Mandruzzato, G., Alfirevic, Z., Chervenak, F., Gruenebaum, A., Heimstad, R., Hainonen, S., Levene, M., Salvesenm K., Saugstad, O., Skupski, D., & Thilanaganathanm B. (2010). Guidelines for the management of post term pregnancy. Journal of Perinatal Medicine, 38(2), 111-9. doi: 10.1515/jpm.2010.057.
Peleg, D., Warsof, S., Wolf, M.F., Perlitz, Y., & Shachar, I.B. (2015). Counseling for fetal macrosomia: an estimated fetal weight of 4000g is excessively low. Am J Perinatol, 32(1), 71-4. doi: 10.1055/s-0034-1376182.
Reed, R. (2019). Post-dates induction of labour: balancing risks. https://midwifethinking.com/2016/07/13/induction-of-labour-balancing-risks/
Todd, A.L., Zhang, L.Y., Khambalia, A.Z., & Roberts, C.L. (2017). Women’s views about the timing of birth. Women and Birth, 30(2), e78-e82. https://doi.org/10.1016/j.wombi.2016.09.002
Wickham, S. (2023). Routine induction in healthy women not supported by evidence. https://www.sarawickham.com/research-updates/routine-induction-in-healthy-women-not-supported-by-evidence/