From time to time, guideline writing groups decide to update their guideline. It isn’t often that there is then research conducted to examine the impact of the changed guideline on the outcomes the guideline was intended to modify. It was therefore a pleasant surprise to read recent research from Sweden that examined the impact of an update to their national fetal monitoring guideline.
Jonsson and colleagues (2022) compared perinatal and maternal outcomes before and after the introduction of a new national fetal monitoring guideline in Sweden in 2017. Based on the International Federation of Gynecology and Obstetrics (FIGO) 2015 guideline, the updated Swedish guideline incorporated assumptions that fetal heart rate patterns assumed to be secondary to compression of the fetal head or umbilical cord were normal rather than pathological features of the CTG trace. Data were obtained from the national Swedish Pregnancy Register, comparing outcomes from 160,210 births between June 2014 and May 2016, and 166,558 births between June 2018 and May 2020. 98.7% of women in the first cohort used CTG monitoring, and 99% in the second cohort. All babies included were born at or after 34 weeks, singleton, cephalic presenting, and born alive. Babies born by prelabour caesarean section or with congenital abnormalities were excluded, as were those not born in a hospital setting. Odds ratios were corrected for known confounders, namely maternal age, education, country of birth, parity, BMI, smoking, oxytocin use, and gestational diabetes.
A small increase in the proportion of babies born with moderate or severe hypoxic ischaemic encephalopathy was noted (rising from 6 to 8 per 10,000 births). The adjusted odds ratio (aOR) was 1.24 and was not statistically significant (95% CI 0.95 – 1.63). There was no significant change in neonatal mortality either (aOR 0.70, 95% CI 0.40-1.22).
Abnormal cord blood gas results were seen more often in the period after the new guideline was introduced (rising from 84 to 119 per 10,000 births, aOR 1.33, 95% CI 1.22-1.44). Apgar scores were more often low in the second period, both scores of under 4 at 5 minutes (rising from 14 to 20 per 10,000 births, aOR 1.36, 95% CI 1.14-1.62) and under 7 at 5 minutes (rising from 81 to 105 per 10,000 births, aOR 1.23, 95% CI 1.14-1.33). More babies experienced neonatal seizures (rising from 13 to 19 per 10,000 births, aOR 1.36, 95% CI 1.14-1.63).
After adjusting for confounders, a very small reduction in caesarean section rates was seen over time (a fall of 0.35%, aOR 0.92, 95% CI 0.89 – 0.95). A small fall in the use of vacuum extraction also occurred (from 6.5% to 5.7%, aOR 0.76, 95% CI 0.74-0.78).
It is always risky to draw conclusions about causation from retrospective population studies. Long term outcomes such as cerebral palsy and cognitive function were not assessed. The authors stated:
Although insignificant, a small increase in HIE grade 2–3 cannot be excluded. Operative deliveries were significantly lower after the introduction of the revised classification. Even though causality cannot be proven, the tendency for a higher frequency of HIE grade 2–3, acidemic newborns and low Apgar scores after introduction of the revised guidelines deserves continued attention. These findings may have several explanations that will need further exploration.p. 191
While the reduction in surgical births after the introduction of the new guideline was beneficial, the rise in cord blood acidosis, lower Apgar scores, and neonatal seizures is concerning. This is not entirely unexpected given that there is increasing recognition that early decelerations and uncomplicated variable decelerations are not secondary to head and cord compression respectively, and are not always benign changes. (I have previously written about the assumptions about head compression here and here, and touched on cord compression here). This research serves as a reminder that fetal monitoring guidelines must be evidence-based and should be assessed to ensure they are fit for purpose.
Jonsson, M., Soderling, J., Ladfors, L., Nordstrom, L., Nilsson, M., Algovik, M., Norman, M., & Holzmann, M. (2022). Implementation of a revised classification for intrapartum fetal heart rate monitoring and association to birth outcome: A national cohort study. Acta Obstetricia et Gynecologica Scandinavica, 101(2), 183-192. https://doi.org/10.1111/aogs.14296