Women with adequate vitamin D status had a 33% higher chance of achieving a live birth than those who were deficient or insufficient, found the research team, a collaboration between Tommy's National Centre for Miscarriage Research, University of Birmingham and Birmingham Women's and Children's NHS Foundation Trust.
Vitamin D sufficiency was considered to be 75 nanomoles per litre (nmol/L), while less than 50 nmol/L was defined as deficient. Serum concentrations between these two levels was considered as insufficient.
The researchers also found that vitamin D sufficiency was linked to better results in other conception related outcomes. The number of women who achieved a positive pregnancy test two weeks after embryo transfer was 34% higher in those with adequate status, compared with vitamin D deficient or insufficient subjects.
Studies which measured ‘clinical pregnancy’ (the presence of a foetal heart beat at approximately five weeks after embryo transfer) found a 46% improvement in outcome in vitamin D-sufficient women.
The review found no link between vitamin D status and rates of miscarriage.
“This systematic review including 11 studies suggests that the chances of achieving a live birth, a positive pregnancy test and clinical pregnancy after assisted reproduction treatment (ART) are higher in women who are vitamin D replete when compared to those who are vitamin D deficient or insufficient. Miscarriage does not appear to be associated with vitamin D status,” wrote lead author Dr. Justin Chu from the University of Birmingham.
Study Details/ Implications
The review and meta-analysis included 11 studies involving 2700 women undergoing fertility treatment (in vitro fertilisation (IVF), intracytoplasmic sperm injection (ICSI) and/or frozen embryo transfer) and whose vitamin D status had been measured through blood tests.
The widespread level of vitamin D inadequacy surprised the researchers.
"One startling finding was the high prevalence of vitamin D deficiency among these women. We found that only 26% of women in the studies had sufficient concentrations of vitamin D; 35% had deficient concentrations and 45% had insufficient concentrations," commented co-author, Dr Ioannis Gallos.
The prevalence of deficiency together with the findings, suggest that treating vitamin D deficiency and insufficiency could be important in women undergoing fertility treatment.
"Testing for vitamin D concentrations is relatively cheap and widely available and its treatment is not costly," said Dr Chu. "It could be that correcting vitamin D deficiency could benefit women undergoing assisted reproduction treatment, but further research is needed to test this."
As all the studies in the review were observational, no causal connection can be attributed to vitamin D’s potential action on pregnancy outcomes.
However, the strength of the associations identified in the meta-analysis prompted the researchers to call for an intervention trial to test the benefits of vitamin D supplementation on pregnancy outcomes in women considering fertility treatment.
“A randomised controlled trial to investigate the benefits of vitamin D deficiency treatment should be considered,” concluded the researchers.
Source: Human Reproduction
Published online, doi: 10.1093/humrep/dex326
“Vitamin D and assisted reproductive treatment outcome: a systematic review and meta-analysis”
Authors: Justin Chu, Ioannis Gallos, Aurelio Tobias, Bee Tan, Abey Eapen, and Arri Coomarasamy