Time to birth for spontaneous and ART births among infertile groups

Childbearing postponement in high-income countries has likely led to an increase in the incidence of age-related infertility. While assisted reproductive technologies (ART) can help some individuals to become parents, this often takes time. However, we know little about how long it takes individuals with infertility problems to achieve a live birth, whether they use ART or not, and how this has changed over time.

We use retrospective information from the HUNT study, which provides rare information on the age at first conception attempt among people who have ever experienced infertility issues. These data are linked to the Norwegian Medical Birth Registry (NMBR), which allows tracking the timing of live births and whether they result from ART. We control for several maternal and paternal characteristics and distinguish between the late 1980-1990s (1987-99) and the 2000-2010s (2000-19). Cox models were fitted to samples of 863 mothers and 590 fathers.

The average time from the start of conception attempt to spontaneous births is three years, and to ART births is five years. ART births occurred faster when pregnancy attempts were initiated in 2000-19 rather than 1987-99 (coeff = 0.536, [0.198; 0.873] for women, coeff = 0.487, [0.072; 0.902] for men), and when men and women tried to conceive for the first time at age 35-39 (coeff = 1.215, [0.260; 2.171] for women, coeff = 1.005, [0.275; 1.735] for men). This was not the case for spontaneous births.

While assisted reproductive technologies enable individuals facing infertility issues to achieve a live birth, they require more time to succeed. However, since the 2000s, time to ART births has decreased, with the shortest observed among those initiating conception attempts in their late thirties. Despite the fact that age remains a significant negative factor associated with the declining occurrence of births, these findings may reflect shifts in the profile of fertility clinic patients, faster care-seeking processes, and improvements in ART efficiency.