Follicle Count and How It Affects Chances of Twin Pregnancy in IUI

What is IUI?

Intrauterine insemination, or IUI, is a type of fertility treatment that helps to increase your chances of pregnancy by placing your partner’s sperm directly into your womb. This procedure is less invasive and is usually recommended as part of initial treatment for couples facing unexplained infertility.

IUI can sometimes result in multiple pregnancies, including twins. The number of mature follicles present during an IUI cycle plays a significant role in determining the likelihood of twins. Let's explore this relationship in more detail.

What is a mature follicle?

A mature follicle is a fluid-filled sac in the ovary that contains a fully developed egg ready for ovulation. The average diameter of a mature follicle is typically between 18 and 25 millimeters. These follicles are also known as dominant follicles or De Graaf follicles.

Mature follicles are composed of several parts:

• The oocyte (egg cell) surrounded by a zona pellucida

• A fluid-filled cavity is visible on ultrasound

• Concentric layers of cells are present, including granulosa cells and theca interna and externa cells.

During a natural menstrual cycle, usually only one follicle reaches full maturity and releases its egg during ovulation, which occurs around day 14 of the cycle. Fertility specialists may give you medications to stimulate the ovaries, making them produce more than one egg.

The size of the follicle is a crucial indicator of egg maturity and readiness for fertilization. Fertility specialists use follicle size measurements to determine the optimal timing for egg retrieval in IUI procedures or to predict natural ovulation.

What does IUI with an increase in follicle count mean?

IUI with an increase in follicle count means that the process of artificial insemination of sperm is directly placed into your uterus when you have more than 1 mature follicle. Therefore, multiple ovarian follicles can supply the egg for fertilisation following the artificial insemination procedure. This increases the likelihood of a successful conception during the IUI cycle compared to a single follicle cycle.

Follicle count and twin risk

The risk of twin pregnancy in IUI increases with the number of mature follicles:

• Single follicle: 

  • With one mature follicle, the risk of twins is similar to natural conception, around 1-2%.

• Two follicles: 

  • The chance of twins increases slightly, with studies showing a 2.5 times higher risk compared to a single follicle.

• Three follicles: 

  • The risk of multiple pregnancies, including twins, rises significantly. The odds of multiples are 3.6 times higher than with one follicle.

• Four or more follicles: 

  • The risk continues to increase, with four follicles showing 4.4 times higher odds and five follicles showing 5 times higher odds of multiples compared to a single follicle.

When you have a higher mature follicle count, your chances of having twins are higher, as each follicle has an egg; if more than one egg gets fertilised, you could end up pregnant with twins. However, more than 60% of twins are born prematurely, and twin pregnancies carry a higher risk of miscarriage, congenital disabilities, gestational hypertension, and anaemia.

This is just a general guide, and everyone is different. Consulting your fertility specialist will help you understand your chances of twins during IUI with an increased follicle count and what to expect during your fertility journey.

It's important to have a thorough consultation with your fertility specialist to determine if IUI is suitable for you. Request a consultation with our fertility specialist at the Thomson Fertility Centre for personalised recommendations and tailored advice.

Age considerations

The impact of follicle count on twin risk varies with age:

• Under 38 years: 

  • More than two mature follicles do not significantly increase singleton pregnancy rates but substantially raise the risk of multiples.

• 38-40 years: 

  • Increasing follicles from one to five raises the clinical pregnancy rate from 9.5% to 16.9% but also increases the multiple pregnancy risk from 0.5% to 3.6%.

• Over 40 years: 

  • The risk of multiples remains relatively low even with higher follicle counts, likely due to decreased egg quality.

How to manage risks?

To balance pregnancy success with the risks associated with multiple pregnancies, many fertility specialists recommend:

• Limiting IUI cycles to no more than two mature follicles for women under 40.

• Consider cancelling IUI cycles if more than three follicles mature, due to the increased risk of higher-order multiples.

• Individualising treatment based on factors such as age, fertility history, and patient preferences.

It's crucial for patients to have thorough discussions with their healthcare providers about the risks and benefits of proceeding with IUI based on their follicle count. While more follicles may increase the chances of pregnancy, they also significantly raise the risk of twins and other multiple pregnancies, which can lead to complications for both mother and babies.

Remember, every patient's situation is unique, and decisions should be made in consultation with a fertility specialist who can provide personalised advice based on individual circumstances.

The information provided is intended for general guidance only and should not be considered medical advice. For personalised recommendations and tailored advice, please consult a specialist at Thomson Medical. Book an appointment with Thomson Medical today.

FAQ

What size follicle will cause twins with IUI?

Follicles measuring 12 mm or wider increase the risk of having a twin or a high-order multiple pregnancy rate.

How common are twins with IUI?

The chances of having twins with IUI are very low. Only around 1.2% of all successful IUI treatments resulted in a multiple pregnancy.

What is the ideal number of follicles for IUI?

Increasing the number of mature follicles from 1 to 5 at the time of IUI in women under 38 years of age increased the clinical pregnancy rate from 14.6% to 21.9%.

How to avoid twins in IUI?

Transferring a single embryo instead of multiple embryos during the IUI procedure can significantly reduce the chances of having twins. This approach, called elective single embryo transfer (eSET), aims to minimise the risks associated with multiple pregnancies while increasing the likelihood of a successful pregnancy.

Does 2 follicles mean 2 eggs?

A common misconception is that each follicle releases multiple eggs. However, as to the question of how many eggs are in a follicle, the answer is just one. This is the scientific process behind ovulation, which generally occurs monthly for most women between puberty and menopause.

Does multiple follicles mean twins?

If several eggs are released and are fertilised by your partner's sperm, you will have an increased chance of multiple pregnancies.

The information provided is intended for general guidance only and should not be considered medical advice. For personalised recommendations and tailored advice, please consult a specialist at Thomson Medical. Book an appointment with Thomson Medical today.