Is conception by in vitro fertilization associated with altered antenatal and postnatal growth trajectories?

Fetal growth after fresh and frozen embryo transfer and natural conception: A population-based register study

OBJECTIVE

To investigate fetal growth trajectories and risks of small and large for gestational age (SGA and LGA), and macrosomia in pregnancies after fresh and frozen embryo transfer (ET), and natural conception (NC).

DESIGN

Longitudinal population-based cohort study.

SETTING

Swedish national registers.

POPULATION

A total of 196 008 singleton pregnancies between 2013 and 2017.

METHODS

Of all singleton pregnancies resulting in live births in the Swedish Pregnancy Register, 10 970 fresh ET, 6520 frozen ET, and 178 518 NC pregnancies with ultrasound data were included. A general least squares model was used to examine the effect of fresh or frozen ET on fetal growth while adjusting for confounders.

MAIN OUTCOME MEASURES

Fetal growth velocity. SGA, LGA and macrosomia.

RESULTS

At 120 days, fetal weights were lower in fresh ET pregnancies compared with NC pregnancies. Thereafter fresh ET as well as FET fetuses had higher fetal weights than NC fetuses, with no differences between themselves until the second trimester. From 210 days, FET fetuses were heavier than fresh ET fetuses, whereas fresh ET fetuses had lower fetal weights than NC fetuses from 245 days. After fresh ET, SGA was more frequent, whereas LGA and macrosomia were less frequent, than after FET.

CONCLUSIONS

This study gives new insights into the differences in fetal growth dynamics between fresh and frozen ET and NC pregnancies. Clinically relevant differences in proportions of SGA, LGA and macrosomia were observed.

The difference in early trimester fetal growth between singletons after frozen embryo transfer and fresh embryo transfer

BACKGROUND

Frozen embryo transfer resulted in a higher birthweight and an increased risk of macrosomia than fresh embryo transfer. However, the mechanism was still unclear. When the impact of frozen embryo transfer on fetal growth began was unknown. Crown-rump length at 11-13 weeks had been regarded as a good indicator of fetal growth in the first trimester and had been used for gestational age calculation in women with uncertain last menstrual periods.

OBJECTIVE

To evaluate the association between frozen embryo transfer and early fetal growth, particularly the crown-rump length, then fresh embryo transfer. The secondary objective was to investigate the potential correlation between crown-rump length and birthweight.

STUDY DESIGN

This was a retrospective cohort study conducted at the Reproductive Medical Center of Shandong University. A total of 4949 patients who obtained singleton pregnancy after frozen embryo transfer and 1793 patients who got singleton pregnancy after fresh embryo transfer between January 1, 2017 and December 31, 2022 were included. The primary outcome was the crown-rump length measured via ultrasound at 11-13 weeks gestation. The secondary outcomes were perinatal outcomes, including birthweight and the risk of large for gestational age, small for gestational age, macrosomia, low birthweight, and premature delivery. Multivariable linear regression models were used to adjust for potential confounders of crown-rump length.

RESULTS

A total of 6742 live singleton births after frozen embryo transfer or fresh embryo transfer were included in this study. In the univariable analysis, the frozen embryo transfer group had a larger crown-rump length (5.75±0.53 cm vs 5.57±0.48 cm, P<.001) and an increased risk of larger-than-expected crown-rump length (13.5% vs11.2%, P=.013) than the fresh embryo transfer group. After adjusting for confounders in multivariable linear regression models, frozen embryo transfer was still associated with a larger crown-rump length (regression coefficient, 3.809 [95% confidence intervals, 3.621-3.997], P<.001). When subgrouped by fetal gender, the crown-rump length of the frozen embryo transfer group was larger than the fresh embryo transfer group in both male and female fetuses. In addition, the crown-rump length was consistently larger in the frozen embryo transfer group than the fresh embryo transfer group in subgroups of the peak estradiol levels. The comparisons among different crown-rump length groups showed that smaller-than-expected crown-rump length was associated with increased risks of small for gestational age (6.3% vs 3.0%, P<.001) and preterm delivery (9.6% vs 6.7%, P=.004) than normal crown-rump length.

CONCLUSION

Frozen embryo transfer was associated with a larger crown-rump length than fresh embryo transfer, suggesting that the effect of frozen embryo transfer on fetal growth may begin in the early trimester. Suboptimal fetal growth in the first trimester may be associated with low birthweight and premature delivery.

Growth of singletons born after frozen embryo transfer until early adulthood: a Finnish register study

STUDY QUESTION

Are there growth differences between singleton children born after frozen embryo transfer (FET), fresh embryo transfer (ET), and natural conception (NC)?

SUMMARY ANSWER

Adolescent boys born after FET have a higher mean proportion and increased odds of overweight compared to those born after fresh ET.

WHAT IS KNOWN ALREADY

Children born after FET have higher mean birthweights and an increased risk of large-for-gestational-age compared to those born after fresh ET and even NC. This raises questions about possible growth differences later in childhood. Previous studies on child growth after FET report partly conflicting results and lack long-term data until adolescence.

STUDY DESIGN, SIZE, DURATION

This was a cohort study based on national population-based registers, the Finnish Medical Birth Register and the Register of Primary Health Care visits, including singletons born after FET (n = 1825), fresh ET (n = 2933), and NC (n = 31 136) in Finland between the years 1995 and 2006.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The proportions of overweight (i.e. age- and sex-adjusted ISO-BMI for children ≥ 25) were compared between the groups. Odds ratios (ORs) and adjusted odds ratios (aORs) of overweight were calculated. Adjustments were made for birth year, preterm birth, maternal age, parity, and socioeconomic status. Mean heights, weights, and BMIs were compared between the groups each year between the ages of 7 and 18.

MAIN RESULTS AND THE ROLE OF CHANCE

FET boys had a higher mean proportion of overweight (28%) compared to fresh ET (22%, P < 0.001) and NC (26%, P = 0.014) boys. For all ages combined, the aOR of overweight was increased (1.14, 95% CI 1.02-1.27) for FET boys compared to fresh ET boys. For girls, the mean proportions of overweight were 18%, 19%, and 22% for those born after FET, fresh ET, and NC, respectively (P = 0.169 for FET vs fresh ET, P < 0.001 for FET vs NC). For all ages combined, FET girls had a decreased aOR of overweight (0.89, 95% CI 0.80-0.99) compared to NC girls. Growth measurements were available for 6.9% to 30.6% of FET boys and for 4.7% to 29.4% of FET girls at different ages.

LIMITATIONS, REASONS FOR CAUTION

Unfortunately, we were not able to adjust for parental anthropometric characteristics. The growth data were not available for the whole cohort, and the proportion of children with available measurements was limited at the start and end of the follow-up. During the study period, mainly cleavage stage embryos were transferred, and slow freezing was used for ART.

WIDER IMPLICATIONS OF THE FINDINGS

The risk of overweight among FET boys warrants further research. Future studies should aim to investigate the mechanisms that explain this sex-specific finding and combine growth data with long-term health data to explore the possible risks of overweight and cardiometabolic disease in adulthood.

STUDY FUNDING/COMPETING INTEREST(S)

Funding was obtained from the Päivikki and Sakari Sohlberg Foundation, the Alma and K.A. Snellman Foundation (personal grants to A.M.T.), and the Finnish Government Research Funding. The funding sources were not involved in the planning or execution of the study. The authors declare no conflicts of interest.

TRIAL REGISTRATION NUMBER

N/A.

Growth of twins conceived using assisted reproductive treatments up to 5 years old: a national growth cohort

STUDY QUESTION

Do twins conceived through assisted reproductive treatments (ART) grow differently from naturally conceived (NC) twins in early life?

SUMMARY ANSWER

Assessments at 6-8 weeks old and at school entry show that ART twins conceived from frozen embryo transfer (FET) grow faster than both NC twins and ART twins conceived from fresh embryo transfer (ET).

WHAT IS KNOWN ALREADY

Singletons born from fresh ET grow more slowly in utero and in the first few weeks of life but then show postnatal catch-up growth by school age, compared to NC and FET babies. Evidence on early child growth of ART twins relative to NC twins is inconsistent; most studies are small and do not distinguish FET from fresh ET cycles.

STUDY DESIGN, SIZE, DURATION

This cohort study included 13 528 live-born twin babies conceived by ART (fresh ET: 2792, FET: 556) and NC (10 180) between 1991 and 2009 in Scotland. The data were obtained by linking Human Fertilisation and Embryology Authority ART register data to the Scottish Morbidity Record (SMR02) and Scottish child health programme datasets. Outcome data were collected at birth, 6-8 weeks (first assessment), and school entry (4-7 years old) assessments. The primary outcome was growth, measured by weight at the three assessment points. Secondary outcomes were length (at birth and 6-8 weeks) or height (at school entry), BMI, occipital circumference, gestational age at birth, newborn intensive care unit admission, and growth rates (between birth and 6-8 weeks and between 6-8 weeks and school entry).

PARTICIPANTS/MATERIALS, SETTING, METHODS

All twins in the linked dataset (born between 1991 and 2009) with growth data were included in the analysis. To determine outcome differences between fresh ET, FET, and NC twins, linear mixed models (or analogous logistic regression models) were used to explore the outcomes of interest. All models were adjusted for available confounders: gestational age/child age, gender, maternal age and smoking, Scottish Index of Multiple Deprivation, year of treatment, parity, ICSI, and ET stage.

MAIN RESULTS AND THE ROLE OF CHANCE

In the primary birth weight models, the average birth weight of fresh ET twins was lower [-35 g; 95% CI: (-53, -16)g] than NC controls, while FET twins were heavier [71 g; 95% CI (33, 110) g] than NC controls and heavier [106 g; 95% CI (65, 146) g] than fresh ET twins. However, the difference between FET and NC twins was not significant when considering only full-term twins (≥37 weeks gestation) [26 g; 95% CI (-30, 82) g], while it was significantly higher in preterm twins [126 g; 95% CI (73, 179) g]. Growth rates did not differ significantly for the three groups from birth to 6-8 weeks. However, FET twins grew significantly faster from 6 to 8 weeks than NC (by 2.2 g/week) and fresh ET twins (by 2.1 g/week). By school entry, FET twins were 614 g [95% CI (158, 1070) g] and 581 g [95% CI (100, 1063) g] heavier than NC and fresh ET twins, respectively. Length/height and occipital frontal circumference did not differ significantly at any time point.

LIMITATIONS, REASONS FOR CAUTION

Although the differences between ART and NC reflect the true ART effects, these effects are likely to be mediated partly through the different prevalence of mono/dizygotic twins in the two groups. We could not explore the mediating effect of zygosity due to the unavailability of data. The confounding variables included in the study were limited to those available in the datasets.

WIDER IMPLICATIONS OF THE FINDINGS

Live-born twins from FET cycles are heavier at birth, grow faster than their fresh ET and NC counterparts, and are still heavier at school entry. This differs from that observed in singletons from the same cohort, where babies in the three conception groups had similar weights by school entry age. The results are reassuring on known differences in FET versus fresh ET and NC twin outcomes. However, FET twins grow faster and are consistently larger, and more ART twins depict catch-up growth. These may lead to an increased risk profile for non-communicable diseases in later life. As such, these twin outcomes require careful evaluation using more recent and comprehensive cohorts.

STUDY FUNDING/COMPETING INTEREST(S)

This study was funded by the EU H2020 Marie Sklodowska-Curie Innovative Training Networks (ITN) grant Dohartnet (H2020-MSCA-ITN-2018-812660). The authors have no competing interests to declare.

TRIAL REGISTRATION NUMBER

N/A.

Greater estimated fetal weight and birth weight in IVF/ICSI pregnancy after frozen-thawed vs fresh blastocyst transfer: prospective cohort study with novel unified modeling methodology

OBJECTIVE

To compare, using a unified approach, standardized estimated fetal weight (EFW) trajectories from the second trimester to birth and birth-weight (BW) measurements in in-vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI) pregnancies obtained after frozen-thawed vs fresh blastocyst transfer (BT).

METHODS

This was a secondary analysis of a prospective longitudinal cohort study performed at the Fetal Medicine and Obstetric Departments of San Raffaele Hospital in Milan, Italy, from January 2016 to December 2020. Eligible for inclusion were singleton viable gestations conceived by autologous IVF/ICSI conception after fresh or frozen-thawed BT that underwent standard fetal biometry assessment at 19-41 weeks and had BW measurements available. All ultrasound assessments were performed by operators blinded to the employment of cryopreservation. Patients with twin gestation, significant pregestational disease, miscarriage, major fetal abnormalities and use of other types of medically assisted reproduction techniques were excluded. EFW and BW Z-scores and their trajectories were analyzed using general linear models (GLM) and logistic regression with a unified modeling methodology based on the Fetal Medicine Foundation fetal and neonatal population weight charts, adjusting for major confounders. Differences between prenatal EFW and postnatal BW centiles in the two groups were assessed and compared using contingency tables, χ² test and conversion of prenatal to postnatal centiles.

RESULTS

A total of 631 IVF/ICSI pregnancies were considered, comprising 263 conceived following fresh BT and 368 after frozen-thawed BT. A total of 1795 EFW observations were available (n = 715 in fresh BT group and n = 1080 in frozen-thawed BT group; median of three observations per patient). EFW and BW < 10^th centile were significantly more frequent in the fresh than in the frozen-thawed BT group (P = 0.003 and P < 0.001, respectively). EFW and BW > 90^th centile were significantly more frequent in the frozen-thawed vs fresh BT group (P = 0.034 and P = 0.002, respectively). GLM showed significantly decreasing EFW Z-scores with advancing gestational age (GA) in both groups. The effect of GA was assumed to be equal in the two study groups, as no significant interaction effect was found. Smoothed mean EFW Z-scores from 19 weeks of gestation to term and smoothed mean BW Z-scores were both significantly higher in the frozen-thawed compared with the fresh BT group (EFW Z-score, 0.70 ± 1.29 vs 0.28 ± 1.43; P < 0.001; BW Z-score, 0.04 ± 1.08 vs -0.31 ± 1.28; P < 0.001). Mean smoothed EFW Z-score values in the frozen-thawed vs fresh BT groups were 1.01 ± 0.12 vs 0.60 ± 0.08 at 19-27 weeks, 0.36 ± 0.07 vs -0.06 ± 0.04 at 28-35 weeks and -0.66 ± 0.01 vs -0.88 ± 0.02 at 36-41 weeks. Mean smoothed BW Z-score values in the frozen-thawed vs fresh BT groups were -0.80 ± 0.14 vs -1.20 ± 0.10 at 28-35 weeks and 0.22 ± 0.16 vs -0.24 ± 0.14 at 36-41 weeks. Assessment of EFW and BW concordance showed a significantly greater rate of postnatal confirmation of prenatally predicted small-for-gestational age (SGA) < 10^th centile in the fresh compared with the frozen-thawed BT group (P < 0.001), whereas the rate of postnatal confirmation of large-for-gestational age (LGA) > 90^th centile was significantly higher in the frozen-thawed vs the fresh BT group (P < 0.001). Logistic regression analysis showed that the smoothed rate of EFW < 3^rd centile was about 6-fold higher in the fresh vs frozen-thawed BT group (P < 0.001), whereas the smoothed rates of EFW 90^th -97^th centile and > 97^th centile were nearly double in the frozen-thawed compared with the fresh BT group (P < 0.05 and P < 0.001, respectively).

CONCLUSIONS

Robust novel unified prenatal-postnatal modeling in IVF/ICSI pregnancies after frozen-thawed or fresh BT from 19 weeks of gestation to birth showed non-divergent growth trajectories, with higher EFW and BW Z-scores in the frozen-thawed vs fresh BT group. The mean EFW Z-scores in both IVF/ICSI groups were greater than those expected for natural conceptions, being highest in the midtrimester and decreasing with advancing gestation in both groups, becoming negative after 32 weeks in the fresh and after 35 weeks in the frozen-thawed BT group. Mean BW Z-scores were negative in both groups, with lower values in preterm fetuses, and increased with advancing gestation, becoming positive at term in the frozen-thawed BT group. IVF/ICSI conceptions from frozen-thawed as compared to fresh BT presented increased rate of LGA and reduced rate of SGA both prenatally and postnatally. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.

Childhood growth of term singletons born after frozen compared with fresh embryo transfer

RESEARCH QUESTION

Is the growth of term singletons born after frozen embryo transfer (FET) comparable to those born after fresh embryo transfer and natural conception up to 5 years of age?

DESIGN

Observational cohort study in an academic medical centre and municipal child health clinics with repeated measurements carried out by medical professionals. Term singletons born after FET (n = 110) and fresh embryo transfer (n = 181) and their matched natural conception controls (n = 543) born in Oulu, Northern Finland, were included. Mean weights, lengths, heights and head circumferences at the ages of 4, 8 and 18 months and 3 and 5 years were compared. At 3 and 5 years, body mass indices were compared.

RESULTS

Childhood growth did not differ between term singletons born after FET, fresh embryo transfer and natural conception, correcting for exact age at measurement and adjusting for maternal body mass index and paternal height.

CONCLUSIONS

Similar growth between children born after FET, fresh embryo transfer and natural conception offers reassurance of the safety and feasibility of the steadily increasing use of embryo cryopreservation in assisted reproduction.