A Retrospective Study Examining Phentermine on Preconception Weight Loss and Pregnancy Outcomes

Obesity is a well-known risk factor for infertility. However, the use of weight loss medications prior to conception is underutilized. The objectives of our study are to describe weight loss, pregnancy rates, and live birth rates after short-term phentermine use in women with obesity and infertility.

This was a retrospective analysis of 55 women (18 to 45 years old) who were overweight or obese, diagnosed with infertility, and prescribed phentermine for weight loss in an ambulatory endocrinology clinic at a single, tertiary level academic medical center. Main outcome measures were mean percent weight change at 3 months after starting phentermine, and pregnancy, and live birth rates from start of phentermine to June 30, 2017.

Median duration of phentermine use was 70 days (Q1, Q3 [33, 129]). Mean ± SD percent weight change at 3 months after starting phentermine was -5.3 ± 4.1% (P<.001). The pregnancy rate was 60% and the live birth rate was 49%. There was no significant difference in pregnancy rates (52% versus 68%; P = .23) or live birth rates (44% versus 54%; P = .50) in women who lost ≥5% versus <5% of their baseline weight. The number of metabolic comorbidities was negatively associated with the pregnancy rate. Phentermine was generally well-tolerated with no serious adverse events.

Phentermine can produce clinically significant weight loss in women with obesity during the preconception period. Higher pregnancy or live birth rates were not observed with a greater degree of weight loss with phentermine.