This case-control study involving fertile and subfertile couples aims to identify male factors related to pregnancy likelihood, create a fertility index measure combining male and female factors to predict pregnancy likelihood, and examine how male factors relate to the semen physical and biological characteristics.

Paternal contributions to fertility and reproductive health outcomes have been understudied, despite promising evidence from animal studies. This study aims to investigate the male contribution to pregnancy likelihood and explore the underlying biological mechanisms. Specifically, the investigators aim to (1) identify male factors associated with pregnancy rate; (2) develop a fertility index combining modifiable factors for both males and females to predict pregnancy rate; and (3) explore the relationship of male modifiable factors with semen physical and molecular characteristics. This is a case-control study with 480 fertile and subfertile males (along with their female partners), recruited from KK Women's and Children's Hospital. The investigators will use questionnaires to collect data on socio-demographic characteristics, clinical, lifestyle, and environmental factors; analyze metabolic and stress biomarkers from blood samples; and measure semen parameters including sperm motility, density, morphology, volume, DNA fragmentation, DNA methylation, gene expression, and seminal plasma oxidative status. Findings from this proposed study will pave the way for developing lifestyle-based or medical interventions to enhance male and couple reproductive health, and potentially benefiting future offspring health.

Inclusion Criteria:

Subfertile couples:

• men aged ≥21-49 years
• men with a female partner aged 21-39 years
• couples who are not able to conceive for at least 12 months
• couples who are Singapore citizen or permanent resident

Fertile couples:

• men aged 21-49 years
• men with a female partner aged 21-39 years
• men with proven fertility defined as those female partners who are currently pregnant and with viable intrauterine pregnancy at gestational weeks of less or equal to 16 at the time of the study
• couples with attempted time to conceive within 12 months to achieve this pregnancy or with unplanned pregnancy
• couples who are Singapore citizen or permanent resident

Exclusion Criteria:

Subfertile couples:

• male infertility of a known aetiology including azoospermia, retrograde ejaculation, genetic disorders, cancer treatment, or testes trauma
• female infertility diagnosis as confirmed by diagnostic imaging or having severe endometriosis
• female partners with irregular menstrual cycle >35 days
• couples with known chromosomal abnormalities

Fertile couples:

• couples who achieve pregnancy after oocyte or spermatozoa donation
• couples with known chromosomal abnormalities
• female partners with known uterine abnormalities

Based on biological sex identity for males and females

The subfertile couples will be recruited from the infertility clinics, while the fertile couples will be recruited from the antenatal clinics. Both groups will also be recruited from on-going preconception and pregnancy programs in the hospital.