Discrimination by parity is a prerequisite for assessing induction of labour outcome – observational study

Objective: To demonstrate that studies on induction of labour should be analyzed by parity as there is a significant difference in the labour outcome among induced nulliparous and multiparous women Methods: Obstetric outcome, specifically caesarean section rates, among induced term nulliparous and multiparous women without a previous caesarean section were analyzed using the Robson 10 group classification 2 for the year 2016. Results: The caesarean rates among nulliparous women in spontaneous and induced labour, Robson groups 1 and 2A, were 7.8% (151/1925) and 32.6% (437/1339) respectively and among multiparous (excluding those women with a previous caesarean section), Robson group 3 and 4A were 1%(24/2389) and 4.4% (44/1005), respectively. Pre labour caesarean rates for nulliparous and multiparous women, Robson groups 2B and 4B 2 were 3.9% (133/3397) and 2.8% (100/3494), of the respective single cephalic cohort at term. Conclusion: The data strongly suggests that studies on induction of labour should be analyzed by parity and should probably be confined to nulliparous women.


Abstract
Objective: To demonstrate that studies on induction of labour should be analyzed by parity as there is a significant difference in the labour outcome among induced nulliparous and multiparous women Methods: Obstetric outcome, specifically caesarean section rates, among induced term nulliparous and multiparous women without a previous caesarean section were analyzed using the Robson 10 group classification 2 for the year 2016.
Conclusion: The data strongly suggests that studies on induction of labour should be analyzed by parity and should probably be confined to nulliparous women.

Background
The overall induction of labour rate in Ireland is 25% 1 . The induction rate among single cephalic nulliparous women, ≥ 37weeks of gestation (SCNT) cohort group has increased in our hospital from 17.5 % when the Robson classification 2 was introduced in 1994 to 39.4 % in 2016 (Table 1). This increase in the induction rate is due to a variety of reasons including, 'prolonged pregnancy', gestational diabetes, cholestasis in pregnancy, patient's request; indications which are usually recurrent and will, most likely, present a problem in subsequent pregnancies for women who have been delivered by caesarean section for failed induction in their first pregnancy.
A PubMed search (years 2010-2016) for publications on induction of labour was performed to determine how many abstracts mentioned parity. A search produced 404 abstracts of which only 77(19.1%) specifically stated that the study was confined to nulliparous or multiparous women. Of the remaining, 136(33.7%) mentioned parity as a variable in the analysis of results and 191 (47.2%) did not mention parity at all.

Methods
This was a retrospective observational study of data collated at the time of delivery on a computer database at the National Maternity Hospital, Dublin. Caesarean rates for Robson term single cephalic nulliparous and multiparous women were taken from data published in the annual hospital report. It is important to note that women with a previous caesarean section were excluded from the analysis. The indication for induction were classified under 6 headings: preeclampsia (hypertension and proteinuria)/ hypertension, postdates >=42 weeks, SROM, maternal reasons/pains, fetal reasons (IUGR, reduced liquor, GDM, obstetric cholestasis and others.) and nonmedical reasons (maternal request for postdates in prolonged pregnancy but not >= 42 weeks). (Table 4) The classification of caesarean section, performed during induction process or after labour was diagnosed, was classified as fetal reasons (without the use of oxytocin) and dystocia (which was further sub classified). 3,4 (Table 5) Following admission for induction of labour a CTG was performed and the cervix was assessed by an experienced obstetrician. When the cervix was thought to be favorable artificial rupture of the membranes was performed (ARM) and an oxytocin infusion was commenced the following day if labour had not commenced.
When the cervix was deemed to be unfavorable, a prostaglandin PGE2 intravaginal gel was administrated and repeated if necessary, in 6 hours provided the repeat CTG were normal. A number of women were treated with Propess instead of PGE2 gel by the same principle. If labour had not commenced by the following day, the induction process was repeated; ARM or prostaglandin gel. When there was no change in cervical status after 2 days of induction process, a caesarean section was performed but was included in Robson group 2A or 4A.

Results
The induction rate among single cephalic nulliparous women at term (SCNT) ( Table 3) Overall the caesarean section rate by indication was lowest in both groups when the indication for induction was for fetal reasons or maternal pains. Among nulliparous women, the highest caesarean section rate by indication were for postdates pregnancies ( = > 42weeks) 44 % and 48% for nonmedical reasons and late pregnancies < 42 weeks. (Table 4) The indications for caesarean sections are shown in table 5 and as expected, the main difference between group 2A and 4A was the number indicated for dystocia and suspected fetal distress. (Table 5).

Discussion
As the number of inductions are seemingly increasing there is a realization that the most significant groups to study are groups 2A and 4A from the Robson classification. In particular though, it is Group 2A.
Nulliparous women are always three to four times more likely to be delivered by Ethics committee approval has been waived as the data used in this study is published in the hospital annual report and therefore, it's accessible to the general public.

CONSENT FOR PUBLICATION:
Not applicable AVAILABILITY OF DATA AND MATERIALS: All the data used in this study is published in hospital annual report.