Cohort profile: a national, population-based cohort of children born after assisted conception in the UK (1992-2009): methodology and birthweight analysis

Perinatal health in a cohort of children conceived after assisted reproduction in the UK: a population-based record-linkage study

OBJECTIVE

To compare the risk of hospitalisation for conditions originating in the perinatal period between children conceived via assisted reproductive technology and those that are naturally conceived, differentiating by treatment type.

STUDY DESIGN, SETTING AND PARTICIPANTS

Population-based record-linkage study of children born after assisted reproduction in the UK between 2002 and 2009 (n=44 618), their naturally conceived siblings (n=8462) and matched naturally conceived population (n=89 072) controls linked to their hospital inpatient records up to 31 March 2016.

PRIMARY AND SECONDARY OUTCOME MEASURES

Robust estimates of the overall and cause-specific risk of hospital admission for adverse perinatal events and the comparison of outcomes by type of treatment.

RESULTS

Over the study period, 17 132 (38.40%) children conceived via assisted reproduction and 30 306 (34.02%) and 1738 (20.54%) naturally conceived population and sibling controls, respectively, were admitted to the hospital for severe perinatal events. Compared with the population controls, singletons (Risk ratio (95% CI 1.30 (1.26, 1.34))) and twins (1.01 (0.99, 1.03)) conceived via assisted reproduction exhibited a higher risk of hospitalisation for any adverse perinatal event. However, no such increase was observed in the within-sibling analysis (0.97 (0.84, 1.12)). Similar patterns were seen for diagnoses related to length of gestation and fetal growth (vs population controls: 1.37 (1.29, 1.46); vs siblings: 1.17 (0.86, 1.60)); birth trauma (vs population controls: 1.23 (1.04, 1.44); vs siblings: 0.78 (0.47, 1.30)); respiratory and cardiovascular disorders (vs population controls: 1.28 (1.20, 1.38); vs siblings: 0.72 (0.53, 0.98)); infections (vs population controls: 1.30 (1.06, 1.59); vs siblings: 0,68 (0.24, 1.90)) and several other conditions. Associations were similar when comparing in vitro fertilisation to intracytoplasmic sperm injection and were higher when comparing fresh to frozen embryo transfers.

CONCLUSION

Children conceived via assisted reproduction showed modest increases in the risk of hospitalisations for severe perinatal events when compared with population controls, although these findings were attenuated in the sibling analyses. The imprecision of within-sibling analyses highlights the need for larger studies to explore potential causal effects.

Long-term outcomes for children conceived by assisted reproductive technology

Worldwide, more than 10 million children have been born after assisted reproduction technology (ART), comprising up to 7.9% of children born in Europe and up to 5.1 % of children born in the US in 2018. The short-term outcome for children born after ART is well-known from numerous publications, with higher rates of preterm birth and low birth weight in children born after fresh embryo transfer and higher rates of large for gestational age and high birth weight in children born after frozen embryo transfer compared with children born after spontaneous conception. Higher rates of birth defects in children born after ART have also been shown consistently over time. Studies on long-term health outcomes after ART are scarcer but suggest an increased risk of altered blood pressure and cardiovascular function in children born after ART. In this review, we summarize long-term health outcomes in children born after ART and discuss whether the increased health risks are associated with intrinsic maternal or paternal factors related to subfertility or ART treatments per se. Finally, we speculate where the future will bring us regarding ART treatment strategies and the safety of the mother and child.

Birth size after embryo cryopreservation: larger by all measures?

STUDY QUESTION

Are the changes in birthweight after frozen and fresh embryo transfer associated with corresponding changes in other measures of foetal growth and placental efficiency?

SUMMARY ANSWER

Although placental efficiency was reduced for both frozen and fresh embryo transfer, children born after frozen embryo transfer (frozen-ET) had symmetrically increased size at birth, whereas children born after fresh embryo transfer (fresh-ET) were asymmetrically smaller at birth, compared to naturally conceived children.

WHAT IS KNOWN ALREADY

In pregnancies following frozen-ET, the risk of being born large, as measured by birthweight, is higher than after natural and fresh-ET conceptions. It is not known whether this is a result of symmetrically increased growth and increased placental efficiency.

STUDY DESIGN, SIZE, DURATION

A Norwegian nationwide registry-based cohort study of 3093 singletons born after frozen-ET, 15 510 singletons born after fresh-ET and 1 125 366 singletons born after natural conception from 1988 to 2015 was performed. We identified 6334 sibships with at least two different conception methods.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Data were collected from the Medical Birth Registry of Norway and the Norwegian National Education Database. Main outcome measures were birth length, birthweight, head circumference, ponderal index (birthweight relative to birth length in kg/m3), placental weight, birthweight:placental weight ratio, gestational age, and birthweight z-score. We estimated mean differences between children born after frozen-ET and fresh-ET compared to natural conception, at the population level and within sibships. Adjustments were made for birth year, maternal age, parity, and education.

MAIN RESULTS AND THE ROLE OF CHANCE

Estimates at the population level and within sibships were consistent for all outcomes, for both fresh and frozen-ET compared to natural conception. Within sibships, children born after frozen-ET had longer mean length (Δ = 0.42 cm, 95% CI 0.29 to 0.55) and head circumference (Δ = 0.32 cm, 95% CI 0.23 to 0.41) at birth, but a similar ponderal index (Δ = 0.11 kg/m3, 95% CI -0.04 to 0.26), compared to naturally conceived. Children born after fresh-ET had a shorter length (Δ = -0.22 cm, 95% CI -0.29 to -0.15) and head circumference (Δ = -0.15 cm, 95% CI -0.19 to -0.10), and lower ponderal index (Δ = -0.15 kg/m3, 95% CI -0.23 to -0.07) at birth compared to natural conception within sibships. Furthermore, mean placental weight was larger after both frozen-ET (Δ = 37 g, 95% CI 28 to 45) and fresh-ET (Δ = 7 g, 95% CI 2 to 13) compared to natural conception within sibships, whereas mean birthweight:placental weight ratio was reduced for both frozen-ET (Δ = -0.11, 95% CI -0.17 to -0.05) and fresh-ET (Δ = -0.13, 95% CI -0.16 to -0.09). A range of sensitivity analyses all gave similar conclusions as the main models, including restriction to full siblings, restriction to single embryo transfer, and adjustment for maternal BMI, height, and smoking.

LIMITATIONS, REASONS FOR CAUTION

Additional adjustment for maternal BMI, height, and smoking was possible only for a small sample of the study population (15%). Data on causes and duration of infertility, as well as treatment details, were limited.

WIDER IMPLICATIONS OF THE FINDINGS

The increased birthweight observed in singletons after frozen-ET is associated with a symmetrically increased birth size and large placentas, also after controlling for maternal factors through sibship analyses. Identifying the responsible treatment factors and the long-term health outcomes are particularly important considering the increase in elective freezing of all embryos.

STUDY FUNDING/COMPETING INTEREST(S)

This work was partly supported by the Central Norway Regional Health Authorities (project number 46045000), the Norwegian University of Science and Technology (project number 81850092) and the Research Council of Norway through its Centres of Excellence funding scheme (project number 262700). The authors have no conflicts of interest to declare.

TRIAL REGISTRATION NUMBER

N/A.

General health in a cohort of children conceived after assisted reproductive technology in the United Kingdom: a population-based record-linkage study

BACKGROUND

Assisted reproductive technology use is increasing annually; however, data on long-term child health outcomes including hospital admissions are limited.

OBJECTIVE

This study aimed to examine the potential effects of assisted reproductive technology on any and cause-specific hospital admissions unrelated to perinatal diagnoses.

STUDY DESIGN

This was a population-based record-linkage study that included a previously established cohort of children born after assisted reproductive technology in the United Kingdom between 1997 and 2009 (n=63,877), their naturally conceived siblings (n=11,343), and matched naturally conceived population controls (n=127,544) linked to their postnatal health outcomes up to March 31, 2016 to provide robust risk estimates of the potential effects of assisted reproductive technology on any and cause-specific hospital admissions unrelated to perinatal diagnoses. In addition, comparison of hospital admissions by type of treatment was made. Cox regression was used to estimate the risk of hospital admission, and negative binomial regression was used to compare the number of hospital admissions per year.

RESULTS

This study had 1.6 million person-years of follow-up (mean, 12.9 years; range, 0-19 years), and the mean age at the time of first hospital admission was 6.5 years (range, 0-19 years). Singletons born after assisted reproductive technology had increased risk of any hospital admission compared with naturally conceived population controls (hazard ratio, 1.08; 95% confidence interval, 1.05-1.10) but not naturally conceived siblings (hazard ratio, 1.01; 95% confidence interval, 0.94-1.09). We observed increased risk of diagnoses related to neoplasms and diseases of the respiratory, musculoskeletal, digestive, and genitourinary systems, and lower risk of injury, poisoning, and consequences of external causes compared with naturally conceived population controls. Children born after intracytoplasmic sperm injection had a lower risk of hospital admission compared with those born after in vitro fertilization, although no such differences were observed between children born after fresh embryo transfers and those born after frozen embryo transfers.

CONCLUSION

Children born after assisted reproductive technology had greater numbers of hospital admissions compared with naturally conceived population controls. Attenuation of these differences in relation to their naturally conceived siblings suggested that this could be partially attributed to the influence of parental subfertility on child health, increased parental concerns, and an actual increase in morbidity in children born after assisted conception.

It is not worth postponing frozen embryo transfers after oocyte pickup: A retrospective cohort study based on propensity score matching

This study was to explore whether postponing frozen embryo transfers (FET) after oocyte pickup (OPU) improves clinical and neonatal outcomes. From May 2018 to Dec 2020, a total of 1109 patients underwent their first OPU cycles adopting a non-selective freeze-all policy were included in this retrospective cohort study. In the immediate group (n=219), patients underwent FET in the first menstrual cycle after OPU, and patients in the postponed group (n=890) waited for more than 1 menstrual cycle after OPU to perform FET. A propensity score matching (PSM) model was used to evaluate the clinical outcomes and neonatal outcomes between the two groups. There were 209 patients in the immediate group and 499 patients in the postponed one after PSM. Patients waited for a significantly shorter period for FET in the immediate group (30.74 ± 3.85 days) compared with the postponed group (80.39 ± 26.25 days, P<0.01). The clinical pregnancy rate (CPR) and live birth rate (LBR) in the immediate group were 58.4% and 48.3%, respectively, which were comparable to those of the postponed one (58.1%, 49.7%, P > 0.05). No statistical significance was found in the average birth weight (3088.82 ± 565.35 g vs 3038.64 ± 625.78 g, P > 0.05) and height (49.08 ± 1.87 cm vs 49.30 ± 2.52 cm) of neonates between the two groups. The gender ratio, the incidence of macrosomia and low birth weight did not differ significantly between the two groups. In conclusion, postponing FET does not improve clinical and neonatal outcomes. If patients have no contraindications, FETs should be carried out immediately after OPU.