Season at the time of oocyte collection and frozen embryo transfer outcomes

STUDY QUESTION

Does the meteorological season at the time of oocyte retrieval affect live birth rates in subsequent frozen embryo transfers?

SUMMARY ANSWER

Frozen embryo transfers resulting from oocytes retrieved in summer have 30% increased odds of live birth compared to frozen embryo transfers resulting from oocytes retrieved in autumn, regardless of the season at the time of embryo transfer.

WHAT IS KNOWN ALREADY

Season at the time of frozen embryo transfer does not appear to be associated with live birth rate. One study in the northern hemisphere found increased odds of live birth with frozen embryo transfer resulting from oocytes collected in summer when compared to those collected in winter.

STUDY DESIGN, SIZE, DURATION

Retrospective cohort study including all frozen embryo transfers performed by a single clinic over eight years, from January 2013 to December 2021. There were 3659 frozen embryo transfers with embryos generated from 2155 IVF cycles in 1835 patients. Outcome data were missing for two embryo transfers, which were excluded from analysis. Outcomes were analysed by the season, temperatures, and measured duration of sunshine at the time of oocyte collection and at the time of frozen embryo transfer.

PARTICIPANTS/MATERIALS, SETTING, METHODS

There were no significant differences between patients with oocyte collection or embryo transfers in different seasons. Meteorological conditions on the day of oocyte collection and the day of frozen embryo transfer, and in the preceding 14- and 28-day periods, were collected including mean, minimum, and maximum temperatures, and recorded duration of sunshine hours. Clinical and embryological outcomes were analysed for their association with seasons, temperatures, and duration of sunshine with correction for repeated cycles per participant, age at the time of oocyte retrieval, and quadratic age.

MAIN RESULTS AND THE ROLE OF CHANCE

Compared to frozen embryo transfers with oocyte retrieval dates in autumn, transfers with oocyte retrieval dates in summer had 30% increased odds of live birth (odds ratio (OR): 1.30, 95% CI: 1.04-1.62) which remained consistent after adjustment for season at the time of embryo transfer. A high duration of sunshine hours (in the top tertile) on the day of oocyte retrieval was associated with a 28% increase in odds of live birth compared to duration of sunshine hours in the lowest tertile (OR 1.28, 95% CI: 1.06-1.53). Temperature on the day of oocyte retrieval did not independently affect the odds of live birth. The odds of live birth were decreased by 18% when the minimum temperature on the day of embryo transfer was high, compared with low (OR: 0.82, 95% CI: 0.69-0.99), which was consistent after correction for the conditions at the time of oocyte retrieval.

LIMITATIONS, REASONS FOR CAUTION

This was a retrospective cohort study, however, all patients during the study period were included and data was missing for only two patients. Given the retrospective nature, causation is not proven and there are other factors that may affect live birth rates and for which we did not have data and were unable to adjust, including pollutants and behavioural factors. We were also not able to stratify results based on specific patient populations (such as poor- or hyper-responders) nor report the cumulative live birth rate per commenced cycle.

WIDER IMPLICATIONS OF THE FINDINGS

These findings may be particularly relevant for patients planning oocyte or embryo cryopreservation. Given the increasing utilization of cryopreservation, identification of factors that influence outcomes in subsequent frozen embryo transfers has implications for future therapeutic and management options. Further studies to clarify the physiology underlying the influence of sunshine hours or season on subsequent frozen embryo transfer outcomes are required, including identification of specific populations that may benefit from these factors.

STUDY FUNDING/COMPETING INTERESTS

No funding was provided for this study. S.L. has received educational travel assistance from Besins, Merck and Organon outside the submitted work. R.H. is National Medical Director of City Fertility and Medical Director of Fertility Specialists of Western Australia, has received honoraria from MSD, Merck Serono, Origio and Ferring outside the submitted work, and has equity interests in CHA SMG. C.R., M.W., and E.N. declare that they have no conflicts of interest.

TRIAL REGISTRATION NUMBER

N/A.

Prophylactic oxytocin for the third stage of labour to prevent postpartum haemorrhage

BACKGROUND

Active management of the third stage of labour reduces the risk of postpartum blood loss (postpartum haemorrhage (PPH)), and is defined as administration of a prophylactic uterotonic, early umbilical cord clamping and controlled cord traction to facilitate placental delivery. The choice of uterotonic varies across the globe and may have an impact on maternal outcomes. This is an update of a review first published in 2001 and last updated in 2013.

OBJECTIVES

To determine the effectiveness of prophylactic oxytocin to prevent PPH and other adverse maternal outcomes in the third stage of labour.

SEARCH METHODS

For this update, we searched Cochrane Pregnancy and Childbirth's Trials Register, ClinicalTrials.gov, WHO International Clinical Trials Registry Platform (ICTRP) (6 March 2019) and reference lists of retrieved studies.

SELECTION CRITERIA

Randomised, quasi- or cluster-randomised trials including women undergoing vaginal delivery who received prophylactic oxytocin during management of the third stage of labour. Primary outcomes were blood loss 500 mL or more after delivery, need for additional uterotonics, and maternal all-cause mortality.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trials for inclusion, extracted data, and assessed trial quality. Data were checked for accuracy. We assessed the quality of the evidence using the GRADE approach.

MAIN RESULTS

This review includes 24 trials, with 23 trials involving 10,018 women contributing data. Due to many trials assessed at high risk of bias, evidence grade ranged from very low to moderate quality.Prophylactic oxytocin versus no uterotonics or placebo (nine trials)Prophylactic oxytocin compared with no uterotonics or placebo may reduce the risk of blood loss of 500 mL after delivery (average risk ratio (RR) 0.51, 95% confidence interval (C) 0.37 to 0.72; 4162 women; 6 studies; Tau² = 0.10, I² = 75%; low-quality evidence), and blood loss 1000 mL after delivery (RR 0.59, 95% CI 0.42 to 0.83; 4123 women; 5 studies; low-quality evidence). Prophylactic oxytocin probably reduces the need for additional uterotonics (average RR 0.54, 95% CI 0.36 to 0.80; 3135 women; 4 studies; Tau² = 0.07, I² = 44%; moderate-quality evidence). There may be no difference in the risk of needing a blood transfusion in women receiving oxytocin compared to no uterotonics or placebo (RR 0.88, 95% CI 0.44 to 1.78; 3081 women; 3 studies; low-quality evidence). Oxytocin may be associated with an increased risk of a third stage greater than 30 minutes (RR 2.55, 95% CI 0.88 to 7.44; 1947 women; 1 study; moderate-quality evidence), however the confidence interval is wide and includes 1.0, indicating that there may be little or no difference.Prophylactic oxytocin versus ergot alkaloids (15 trials)It is uncertain whether oxytocin reduces the likelihood of blood loss 500 mL (average RR 0.84, 95% CI 0.56 to 1.25; 3082 women; 10 studies; Tau² = 0.14, I² = 49%; very low-quality evidence) or the need for additional uterotonics compared to ergot alkaloids (average RR 0.89, 95% CI 0.43 to 1.81; 2178 women; 8 studies; Tau² = 0.76, I² = 79%; very low-quality evidence), because the quality of this evidence is very low. The quality of evidence was very low for blood loss of 1000 mL (RR 1.13, 95% CI 0.63 to 2.01; 1577 women; 3 studies; very low-quality evidence), and need for blood transfusion (average RR 1.37, 95% CI 0.34 to 5.51; 1578 women; 7 studies; Tau² = 1.34, I² = 45%; very low-quality evidence), making benefit of oxytocin over ergot alkaloids uncertain. Oxytocin probably increases the risk of a prolonged third stage greater than 30 minutes (RR 4.69, 95% CI 1.63 to 13.45; 450 women; 2 studies; moderate-quality evidence), although it is uncertain if this translates into increased risk of manual placental removal (average RR 1.10, 95% CI 0.39 to 3.10; 3127 women; 8 studies; Tau² = 1.07, I² = 76%; very low-quality evidence). Oxytocin may make little or no difference to risk of diastolic blood pressure > 100 mm Hg (average RR 0.28, 95% CI 0.04 to 2.05; 960 women; 3 studies; Tau² = 1.23, I² = 50%; low-quality evidence), and is probably associated with a lower risk of vomiting (RR 0.09, 95% CI 0.05 to 0.14; 1991 women; 7 studies; moderate-quality evidence), although the impact of oxytocin on headaches is uncertain (average RR 0.19, 95% CI 0.03 to 1.02; 1543 women; 5 studies; Tau² = 2.54, I² = 72%; very low-quality evidence).Prophylactic oxytocin-ergometrine versus ergot alkaloids (four trials)Oxytocin-ergometrine may slightly reduce the risk of blood loss greater than 500 mL after delivery compared to ergot alkaloids (RR 0.44, 95% CI 0.20 to 0.94; 1168 women; 3 studies; low-quality evidence), based on outcomes from quasi-randomised trials with a high risk of bias. There were no maternal deaths reported in either treatment group in the one trial that reported this outcome (RR not estimable; 1 trial, 807 women; moderate-quality evidence). Need for additional uterotonics was not reported.No subgroup differences were observed between active or expectant management, or different routes or doses of oxytocin for any of our comparisons.

AUTHORS' CONCLUSIONS

Prophylactic oxytocin compared with no uterotonics may reduce blood loss and the need for additional uterotonics. The effect of oxytocin compared to ergot alkaloids is uncertain with regards to blood loss, need for additional uterotonics, and blood transfusion. Oxytocin may increase the risk of a prolonged third stage compared to ergot alkaloids, although whether this translates into increased risk of manual placental removal is uncertain. This potential risk must be weighed against the possible increased risk of side effects associated with ergot alkaloids. Oxytocin-ergometrine may reduce blood loss compared to ergot alkaloids, however the certainty of this conclusion is low. More high-quality trials are needed to assess optimal dosing and route of oxytocin administration, with inclusion of important outcomes such as maternal mortality, shock, and transfer to a higher level of care. A network meta-analysis of uterotonics for PPH prevention plans to address issues around optimal dosing and routes of oxytocin and other uterotonics.

Acute tocolysis for uterine tachysystole or suspected fetal distress

BACKGROUND

Uterine tachysystole (more than 5 contractions per 10 minutes in 2 consecutive intervals) is common during labour, particularly with use of labour-stimulating agents. Tachysystole may reduce fetal oxygenation by interrupting maternal blood flow to the placenta during contractions. Reducing uterine contractions may improve placental blood flow, improving fetal oxygenation. This review aimed to evaluate the use of tocolytics to reduce or stop uterine contractions for improvement of the condition of the fetus in utero. This new review supersedes an earlier Cochrane Review on the same topic.

OBJECTIVES

To assess the effects of the use of acute tocolysis during labour for uterine tachysystole or suspected fetal distress, or both, on fetal, maternal and neonatal outcomes.

SEARCH METHODS

We searched Cochrane Pregnancy and Childbirth's Trials Register, ClinicalTrials.gov and the WHO International Clinical Trials Registry Platform (ICTRP) (2 February 2018), and reference lists of retrieved studies.

SELECTION CRITERIA

Randomised controlled trials (RCTs) evaluating acute tocolysis for uterine tachysystole, intrapartum fetal distress, or both.

DATA COLLECTION AND ANALYSIS

We used standard methods expected by Cochrane.

MAIN RESULTS

We included eight studies (734 women), conducted in hospital settings, predominantly in high-income countries (USA, Austria, Uruguay). Two trials were conducted in upper and lower middle-income countries (South Africa, Sri Lanka). The hospital facilities all had the capacity to perform caesarean section. Overall, the studies had a low risk of bias, except for methods to maintain blinding. All of the trials used a selective beta₂ (ß₂)-adrenergic agonist in one arm, however the drug used varied, as did the comparator. Limited information was available on maternal outcomes.Selective ß₂-adrenergic agonist versus no tocolytic agent, whilst awaiting emergency deliveryThere were two stillbirths, both in the no tocolytic control group (risk ratio (RR) 0.23, 95% confidence interval (CI) 0.01 to 4.55; 2 studies, 57 women; low-quality evidence). One had gross hydrocephalus and the second occurred with vaginal delivery after waiting 55 minutes for caesarean section. The decision for caesarean section delivery was an inclusion criterion in both studies so we could not assess this as an outcome under this comparison. Abnormal fetal heart trace is probably lower with tocolytic treatment (RR 0.28, 95% CI 0.08 to 0.95; 2 studies, 43 women; moderate-quality evidence). The effects on the number of babies with Apgar score below seven were uncertain (low-quality evidence).Intravenous (IV) atosiban versus IV hexoprenaline (1 study, 26 women) One infant in the hexoprenaline group required > 24 hours in the neonatal intensive care unit (NICU) following a forceps delivery (RR 0.33, 95% CI 0.01 to 7.50; low-quality evidence). There were no fetal or neonatal mortalities and no Apgar scores below seven. There was one caesarean delivery in the IV hexoprenaline group (RR 0.33, 95% CI 0.01 to 7.50; low-quality evidence), and one case of abnormal fetal heart score in the atosiban group (RR 3.00, 95% CI 0.13 to 67.51; very low-quality evidence).IV fenoterol bromhydrate versus emergency delivery (1 study, 390 women) No data were reported for perinatal death, severe morbidity or fetal or neonatal mortality. IV fenoterol probably increases the risk of caesarean delivery (RR 1.12, 95% CI 1.04 to 1.22; moderate-quality evidence). Fenoterol may have little or no effect on the risk of Apgar scores below seven (RR 1.28, 95% CI 0.35 to 4.68; low-quality evidence).IV hexoprenaline versus no tocolytic agent, whilst awaiting emergency delivery (1 study, 37 women) No data were reported for perinatal death or severe morbidity. There were two fetal deaths in the no tocolytic control group (RR 0.23, 95% CI 0.01 to 4.55; low-quality evidence). The rate of caesarean delivery was not reported. There were two babies with Apgar scores below seven in the control group and none in the hexoprenaline group (RR 0.24, 95% CI 0.01 to 4.57; 35 women; low-quality evidence).Subcutaneous terbutaline versus IV magnesium sulphate (1 study, 46 women)No data were reported for perinatal death, severe morbidity or fetal or neonatal mortality. The decision for caesarean section was an inclusion criterion, so we could not assess this. The effects on abnormal fetal heart trace are uncertain (very low-quality evidence).Subcutaneous terbutaline with continuation of oxytocic infusion versus cessation of oxytocic infusion without tocolytic agent (1 study, 28 women) No data were reported for perinatal death, severe morbidity or fetal or neonatal mortality. There may be little or no difference in the rates of caesarean delivery in the subcutaneous terbutaline (8/15) and control groups (4/13) (RR 1.73, 95% CI 0.68 to 4.45; low-quality evidence). There were no cases of Apgar scores below seven or abnormal fetal heart trace.Subcutaneous terbutaline versus no tocolytic agent, whilst awaiting emergency delivery (1 study, 20 women) No data were reported for perinatal death or severe morbidity. There were no fetal or neonatal mortalities. The decision for caesarean section was an inclusion criterion, so we could not assess this. There were two babies with Apgar scores below seven in the control group and none in the terbutaline group (RR 0.17, 95% CI 0.01 to 3.08; low-quality evidence).IV terbutaline versus IV nitroglycerin (1 study, 110 women)No data were reported for perinatal death or severe morbidity or fetal or neonatal mortality. There may be little or no difference in the rates of caesarean delivery between the IV terbutaline (30/57) and control groups (29/53) (RR 0.96, 95% CI 0.68 to 1.36; low-quality evidence). There were no cases of Apgar scores below seven.

AUTHORS' CONCLUSIONS

There is insufficient evidence to determine the effects of tocolytics for uterine tachysystole or suspected fetal distress during labour. The clinical significance for some of the improvements in measures of fetal well-being with tocolytics is unclear. The sample sizes were too small to detect effects on neonatal morbidity, mortality or serious adverse effects. The majority of studies are from high-income countries in facilities with access to caesarean section, which may limit the generalisability of the results to lower-resource settings, or settings where caesarean section is not available.Further well-designed and adequately powered RCTs are required to evaluate clinically relevant indicators of maternal and neonatal morbidity and mortality.