Infertility Research Summaries

Director of fertility services at UC San Diego Health, Sanjay Agarwal, MD, writes summaries of new medical research in the field of infertility. These medical studies have been published in medical journals all over the world.

Obesity Reduces Uterine Receptivity

Clinical experience from 9,587 first cycles of ovum donation with normal weight donors.

Obesity affects reproductive performance in many ways. We have known that being overweight can interfere with ovulation and thus produce problems with fertility.

This study evaluated the impact of weight on another important reproductive process – that of implantation. Implantation is the process by which the fertilized egg (embryo) attaches and enters the uterus.

The study evaluated:

  • In-vitro fertilization cycles (in which egg donors were used).
  • Pregnancy rates based on body mass index (BMI) of the woman receiving the embryos.

Because egg donors tend to be young, their embryos are typically of good quality and have a high chance of success. This study found that the higher a woman’s BMI, the lower her chance of pregnancy. This was particularly the case for women with a BMI > 30 kg/m2.

What This Means for You

Based on this and other studies, if you are planning to conceive (either naturally or with assistance), try to get your BMI in the normal range.

A normal BMI (< 25 kg/m2) will help improve your chance of having a healthy pregnancy for both you and your baby.

Fertility and Sterility 2013 Vol 100(4)
Dr. J. Bellver et al. (Spain)

Optimal Follicular Size

What is the optimal follicular size before triggering ovulation in intrauterine insemination cycles with clomiphene citrate or letrozole? An analysis of 988 cycles.

In the normal menstrual cycle, a follicle grows each month. When the follicle reaches about 20mm in diameter, it spontaneously releases an egg. This is called ovulation.

Some women who require help conceiving need to take fertility drugs such as clomiphene citrate (Clomid) or letrozole (Femara) in order to ovulate. These drugs are taken in the early part of the menstrual cycle and help stimulate the growth of a follicle and subsequent ovulation.

Ultrasound scans can be performed to see if the follicle grows properly. If the release of the egg doesn’t occur naturally, a hormone (human chorionic gonadotropin – hCG) is administered to initiate the process.

This study evaluated how triggering ovulation with hCG at different follicle sizes affected pregnancy rate. It was determined that the chance of pregnancy is slightly improved if ovulation is triggered when the largest follicle reaches over 22mm in diameter.

What This Means For You

If you are undergoing fertility treatment with either Clomid or letrozole medications, it is likely that you will have a better chance of achieving pregnancy if your largest follicle is over 22mm in diameter. 

Unfortunately, this is not always possible. For example, your body may trigger ovulation naturally before you are able to reach this follicle size. Alternatively, your doctor may need to trigger ovulation earlier to reduce your risk of multiple pregnancy.

Fertility and Sterility. 2012 May;97(5):1089-94.e1-3
Palatnik A, Strawn E, Szabo A, Robb P. (USA)

Read the full study on the National Institutes of Health.

Letrozole vs. Clomiphene for Infertility in the Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is a hormonal disorder that affects 5 to 10 percent of premenopausal women, and is the primary cause of ovulation problems in women of reproductive age. Women who have PCOS commonly have an irregular or absent period, high levels of testosterone, and often need help conceiving.

Typically, the first line of treatment for women with PCOS who have trouble ovulating is clomiphene (e.g., Clomid), a non-steroidal fertility medicine. However, in 2001, Robert Casper, MD, who did his fertility training at UC San Diego, published a report indicating that letrozole – a medicine used to treat breast cancer and not approved by the FDA in the treatment of fertility – helps women with PCOS ovulate. Since that initial report, several other clinical studies have suggested that letrozole, may be superior for stimulating ovulation.

Recently, a large-scale clinical trial funded by the National Institutes of Health (NIH) compared the rate of pregnancy in women who are treated with letrozole to those treated with clomiphene. These two medicines were randomly given to 750 infertile women diagnosed with PCOS; neither the patient nor their physician knew which of the two medicines was being prescribed.

While both groups had about a 30 percent miscarriage rate, the study found a higher occurrence of ovulations and pregnancies in the letrozole group than the clomiphene group. More importantly, women taking letrozole had an overall 44 percent increased chance of a live birth compared to those taking clomiphene.

What This Means For You

Based on the evidence from this clinical study, if you have PCOS, you are more likely to ovulate and have a live birth with letrozole than with clomiphene.

The fertility experts at UC San Diego Health are working on switching patients who are currently receiving clomiphene for ovulation difficulties to letrozole-based treatment.

The New England Journal of Medicine. July 10, 2014
Legro RS, et al. (USA)

Read the full study on The New England Journal of Medicine.


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