Higher rates of adverse birth outcomes have been consistently reported among children conceived via assisted reproductive technology (ART) compared with children conceived through natural conception. Higher rates of multiple births in ART pregnancies partially explain the increased risk. It remains unclear to what extent the remaining difference can be attributed to the reproductive technology or to factors related to infertility, which is associated with an elevated risk of poorer birth outcomes. Same-sex lesbian couples undergo ART treatments generally without experiencing infertility. To distinguish the effects of reproductive treatment and infertility, we compared birth outcomes in ART pregnancies among same-sex lesbian couples vs natural conceptions and ART pregnancies among heterosexual couples.

Methods: In Sweden, same-sex lesbian couples have been eligible to receive publicly funded ART treatments with donated sperm since 2005. This study included all births in Sweden from 2007 to 2018. Using pseudonymized personal identifiers, the Swedish National Quality Registry for Assisted Reproduction, which includes all ART treatments (in vitro fertilization [IVF], intracytoplasmic sperm injection [ICSI], and intrauterine insemination [IUI]), was linked to the medical birth register and the total population registers, which include information on birth outcomes and sociodemographic characteristics. We focused on first live births for ART and naturally conceived births because 97.3% of ART births among same-sex lesbian couples were first births. We analyzed 4 outcomes: birth weight (continuous), gestational age (continuous), low birth weight (binary, <2500 g), and preterm delivery (binary, <37 weeks of gestation). We estimated linear models on the continuous outcomes and linear probability models on the binary outcomes comparing ART-conceived births among same-sex lesbian couples (reference category) with ART births and naturally conceived births among heterosexual couples. For each outcome, we estimated unadjusted and adjusted (controlling for child sex, multiplicity, and maternal age at birth) models. We also estimated differences focusing on children conceived via IVF/ICSI because 99.4% of ART births among heterosexual couples were conceived via IVF/ICSI compared with 63.3% in same-sex couples, as same-sex couples often start treatments with IUI, which has a lower chance of success regardless of subfertility.

Analyses were conducted using R version 4.1.1 (R Foundation). Statistical significance was set at P < .05 (2-sided). This study was approved by the Regional Ethical Review Board of Stockholm. Informed consent was not required for pseudonymized data.

Results: During the study period, there were 868 ART births among same-sex lesbian couples, 23 488 ART births among heterosexual couples, and 456 898 naturally conceived births. ART-conceived births from same-sex and heterosexual couples showed a higher proportion of multiplicity (5.8% and 7.5%, respectively) than naturally conceived births (2.1%) (Table 1). Couples who conceived naturally had significantly lower birth weight and gestational age and similar risk of low birth weight and preterm delivery compared with same-sex couples who conceived via ART (Table 2). For example, birth weight was 3429.5 g in naturally conceived births vs 3460.2 g in same-sex ART births (adjusted difference, −76.2 g [95% CI, −113 to −39.3 g]; P < .001; low birth weight, 4.9% vs 6.7%, adjusted difference, 0.28 [95% CI, −1.11 to 1.66] percentage points; P = .70). Heterosexual couples who conceived via ART had statistically significantly lower birth weight and gestational age than same-sex couples (eg, birth weight: 3342.9 g vs 3460.2 g; adjusted difference, −97.4 g [95% CI, −134.8 to −59.9 g]; P < .001). Percentages of low birth weight and preterm birth were higher in ART conceptions among heterosexual couples vs same-sex couples but did not reach statistical significance (eg, low birth weight: 8.9% vs 6.7%; adjusted difference, 1.23 [95% CI, −0.17 to 2.65] percentage points; P = .09). The results were qualitatively similar when only considering IVF/ICSI-conceived children (Table 2).

Discussion: This study demonstrated that same-sex lesbian couples undergoing ART had more favorable or similar birth outcomes to heterosexual couples who conceived naturally or underwent ART to conceive, suggesting that infertility-related factors rather than reproductive treatments contribute to higher rates of adverse birth outcomes in ART pregnancies. Limitations of the study include that the presence of infertility factors was not directly assessed and the relatively small sample size of same-sex couples reduced the statistical power of the study, particularly in the binary outcomes analyses.