Are recurrent episodes of RFM a real risk for stillbirth?
If ‘pathological’ RFMs is preterminal, it would seem unlikely that babies repeatedly become very sick and then recover. Indeed, not all evidence supports recurrent ‘episodes’ as a risk 7,9, and not all national (eg US) guidelines support the concept. Recently, in a retrospective study including >8000 pregnancies with RFMs, Turner et 1 reported that two or more episodes might increase stillbirth risk (aOR 4.96; 0.98-24.98) when compared to one episode, yet not when compared to no episodes. In a case control study of 660 stillbirths, Heazell et al 10 reported that women who had experienced stillbirth were more likely than controls to report multiple episodes of RFMs since 26 weeks (OR for three or more episodes 5.11 (3.22 to 8.10)). Ultrasound based studies show conflicting results but generally report a small excess of markers of FGR.
Do these establish recurrent RFMs as an independent risk factor? It constituted a cornerstone of the strategies of the trials that failed to reduce stillbirth. There is huge potential for reverse causality and bias. Women with high-risk pregnancies, or indeed abnormal scan findings, would be expected to be more vigilant, be scanned more often and have SGA babies more often. Women interviewed after a stillbirth may be affected by recall bias. Finally, what is the definition of ‘recurrent’? No analyses differentiate between episodes of RFM and presentations of RFM. Why does this matter? Many clinicians will have seen pregnancies with RFMs and a normal CTG who, less than two days later and usually with continued RFMs, present with the baby in extremis or tragically dead. CTG changes are preterminal but the temporal relationship with RFMs is not consistent. Hence it is worth encouraging re-presentation and repeating the CTG if RFMs continue because the baby may be very sick but the CTG is not yet abnormal. This is not recurrent episodes of RFMs: it is recurrent presentations of one episode.