Smoking and recurrent pregnancy loss: A cohort study of 2829 women.

Smoking during pregnancy is associated with negative reproductive outcome. Less is known about the impact of smoking or previous smoking in women with recurrent pregnancy loss (RPL) which this study aimed to investigate. We included all women <42 years (n=2829) referred to a RPL unit at Copenhagen University Hospital between January 2000 and December 2021 in the cohort with follow-up until June 2022. Patients were categorized as 'smokers at time of referral', 'never-smokers' or 'former smokers'. The main outcomes were pregnancy history prior to referral, prospective pregnancy rate, live birth rate, rates of ectopic pregnancy, and stillbirth. At referral, smokers (n=373) were on average 2.0 years younger (P<0.001) and had experienced significantly more pregnancy losses (P<0.001), and stillbirths (P=0.01) compared to never-smokers (n=2100). Former smokers had a higher risk of stillbirth prior to referral compared to never-smokers but no differences in pregnancy rate or other outcomes. Prospective pregnancy rates were lower for smokers compared with never-smokers (71.8% vs. 77.5%, P=0.02). Live birth rate was 58.0% for the 243 women who smoked at referral compared to 61.4% for the 1488 never-smokers (P=0.32). Stillbirth and ectopic pregnancies were significantly more common for smokers (2.8% vs. 0.4%, P=0.01; 6.0% vs. 2.0%, P<0.008). Women with RPL who smoked at referral were referred younger with a higher number of previous pregnancy losses and stillbirths compared with never-smokers. Fewer smokers achieved a pregnancy after referral but those who did had a similar live birth rate compared to never-smokers, although stillbirths and ectopic pregnancies were more common.

Determinants of monozygotic twinning in ART: a systematic review and a meta-analysis.

BACKGROUND: The incidence of monozygotic twins (MZT) after ART appears to be higher than the incidence after spontaneous conceptions contradicting the aim of ART to avoid multiple pregnancies because of the associated risks. OBJECTIVE AND RATIONALE: The aim was to study the frequency of MZT after IVF and ICSI and how it is influenced by the day of embryo transfer, maternal age, zona pellucida manipulation, controlled ovarian stimulation, stimulation protocol, culture media and embryo quality. SEARCH METHODS: Original studies and reviews were identified by searching the PubMed, Embase and Cochrane databases up to March 2017. The inclusion criterion was publications focusing on the five study questions related to MZT in our study. The exclusion criteria were articles that did not include blastocyst transfer, were on non-humans, were not published in peer-reviewed journals, and were based only on case studies. All of the articles were categorized according to the Oxford Centre for Evidence-based Medicine's 'Levels of Evidence', and quality and risk of bias assessment was performed with 'The Cochrane Collaboration's Risk of Bias Tools'. A meta-analysis was performed to study the impact of the day of embryo transfer on the MZT rate. OUTCOMES: The literature search resulted in a total of 42 articles, including 38 original studies, for analysis. The included original studies reported a MZT rate with blastocyst transfer from zero to 13.2%. Our meta-analysis found a higher frequency of MZT after blastocyst transfer compared with cleavage-stage embryos transfer: odds ratio = 2.18, 95% CI: 1.93-2.48 (fixed effect meta-analysis). A younger maternal age may increase the MZT rate, and recent studies regarding the use of zona pellucida manipulating techniques have disagreed with the previous suspicion of a higher MZT rate after the use of these methods. The extended culture to-blastocyst stage is a potential risk factor for MZT, but it is uncertain whether this phenomenon is due to the extended time, culture media or greater likelihood of younger oocytes to reach the blastocyst stage. An increased frequency of MZT following the GnRH-agonist suppression protocol has been suggested, as well as a decreased frequency of MZT with high gonadotrophin doses, which could reflect an age-related effect. Only limited literature has focused on the role of embryo morphology in the MZT rate, therefore, this issue remains unresolved. WIDER IMPLICATIONS: We found blastocyst transfer to be a risk factor for MZT. Hence, the results of this meta-analysis may weaken the previously proposed view that greater experience with blastocyst transfer and improved culture media could decrease the high rate of MZT after blastocyst transfer. To minimize the rate of MZT and the associated complications, the mechanisms underlying blastocyst transfer and MZT pregnancy must be elucidated.