Getting Pregnant with Twins from Clomid®: What Are Your Chances?
If you’re considering ovulation induction treatment such as Clomid® tablets, your healthcare provider should walk you through all potential side effects and risks of treatment. This includes nausea, bloating, hot flashes, and even having twins .
By OBGYN and fertility expert Dr Kenosha Gleaton
What is clomiphene citrate used for?
First, let’s quickly recap what ovulation is and how it relates to pregnancy. About once a month, a mature egg is released from an ovary and awaits fertilization. This is known as ovulation, and occurs due to the release of two main hormones known as luteinizing hormone (LH) and follicle stimulating hormone (FSH).  Sometimes ovulation doesn’t occur during a menstrual cycle. This is known as anovulation and happens occasionally. Anovulation may also occur if someone has abnormal hormone levels, a condition such as polycystic ovary syndrome (PCOS), or other conditions.
Clomiphene citrate is a medication often used for inducing ovulation in those assigned female at birth that are hoping to conceive.  Not everyone can benefit from ovulation induction medications, but those not ovulating regularly or struggling with infertility may be good candidates for Clomid® or other medications. 
How do ovulation induction medications work?
Ovulation induction medications work in various ways, all with the common goal of stimulating the ovaries to produce and release one or more mature eggs.  Clomiphene is an oral tablet used to induce ovulation, another commonly used medication is letrozole, although letrozole is used off-label for ovulation induction (read more about letrozole for ovulation induction).  There are also injection options available that often have stronger effects and are reserved for certain conditions.
Clomiphene citrate is what we call an estrogen modulator, and it works by blocking estrogen receptors in the brain.  This tells the body that estrogen levels are low and that production of estrogen-boosting hormones (LH and FSH) needs to increase. These hormones then help the body produce and release mature eggs from the ovary. 
Clomiphene citrate and likelihood of conceiving twins
Clomid® and other ovulation induction medications have been associated with multiple pregnancies, such as twins or triplets. [7,12] In fact, almost one third of all twin births in the United States are attributed to some sort of fertility treatment, including IVF, ovulation induction, etc.  Research on clomiphene citrate shows a multiple pregnancy rate ranging from 6% to 11.7%. [7,12] The chances of multiples increases with use of fertility medications because the high hormone levels may cause the ovaries to release more than one egg.
Other factors that may increase chances of twins
Assisted reproduction is one of the leading causes of multiple pregnancies, but there are other factors that can increase the chance of having twins as well:
Those that conceive later in life are more likely to conceive multiples than those conceiving under the age of 30.  This is likely due to the increase in hormones such as FSH. Similarly to what happens with clomiphene citrate and other medications, high levels of hormones cause multiple eggs to be released.
Have you ever noticed that twins sometimes run in the family? That’s no coincidence; there are data that suggest a family history of fraternal twins increases the chance of carrying and fathering fraternal twins. [5-6] To be exact, the rate is about one per 60 in females and one per 125 in men with a family history, compared to one per 250 for the general population. [5-6]
Some research suggests that those overweight are slightly more likely to conceive twins than those of average weight.  Additional body fat may impact hormone levels and cause the release of more than one egg during ovulation.
IVF, IUI, and more
As previously mentioned, assisted reproductive technology is one of the leading causes of multiple pregnancies.  This was especially common with IVF in previous years when more than one embryo was transferred into the uterus. Now it’s less common for providers to suggest transferring more than one embryo. Other fertility drugs and treatments may increase the chance of twins or triplets through ovarian stimulation. 
What to keep in mind
Many people may love the idea of having twins, but there are some things to keep in mind about twin pregnancies. Risks associated with pregnancy do increase when pregnant with multiples, meaning you may be at a higher risk of preterm birth, intrauterine growth restriction, preeclampsia, diabetes, birth complications, and more.  There truthfully isn’t much you can do to change your chances of having twins, but it is important to have an open and honest conversation with your healthcare provider about what a multiple pregnancy could mean for you and your health.
- Clomid® is an ovulation induction medication used to encourage the growth and release of one or more eggs.
- Ovulation induction medications aren’t right for everyone, but may be useful for those having trouble with regular ovulation and are hoping to conceive.
- Clomid® works by increasing the production of two vital hormones, LH and FSH. These hormones work to stimulate ovulation and may result in more than one egg being released, which can cause a multiple pregnancy.
- The chances of conceiving twins on clomiphene citrate is estimated to be about 6% to 11.7%.
- Other factors that increase the chance of a twin pregnancy are weight, age, and family history.
- Legro R S, Brzyski R G, Diamond M P. Letrozole versus Clomiphene for Infertility in the Polycystic Ovary Syndrome. N Engl J Med 2014; 371:119-129. DOI: 10.1056/NEJMoa1313517
- Holesh JE, Bass AN, Lord M. Physiology, Ovulation. [Updated 2022 May 8]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK441996/
- Hamilton-Fairley D, Taylor A. Anovulation. BMJ. 2003;327(7414):546-549. doi:10.1136/bmj.327.7414.546
- Mbi Feh MK, Wadhwa R. Clomiphene. [Updated 2022 Jun 27]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK559292/
- Multiple Pregnancy and Birth: Twins, Triplets, and High-order Multiples. A Guide for Patients. American Society for Reproductive Medicine. 2012. Accessed March 2023. URL.
- S. Lazarov, L. Lazarov, N. Lazarov. MULTIPLE PREGNANCY AND BIRTH: TWINS, TRIPLETS AND HIGH-ORDER MULTIPLES. OVERVIEW. Trakia Journal of Sciences, No 1, pp 103-107, 2016. doi:10.15547/tjs.2016.01.015.
- Garthwaite H, Stewart J, Wilkes S. Multiple pregnancy rate in patients undergoing treatment with clomifene citrate for WHO group II ovulatory disorders: a systematic review. Hum Fertil (Camb). 2022;25(4):618-624. doi:10.1080/14647273.2021.1872803
- Gill P, Lende MN, Van Hook JW. Twin Births. [Updated 2022 Oct 13]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from URL
- McLennan AS, Gyamfi-Bannerman C, Ananth CV, et al. The role of maternal age in twin pregnancy outcomes. Am J Obstet Gynecol. 2017;217(1):80.e1-80.e8. doi:10.1016/j.ajog.2017.03.002
- de la Calle M, Bartha JL, Marín C, et al. Maternal Obesity in Twin Pregnancy: The Role of Nutrition to Reduce Maternal and Fetal Complications. Nutrients. 2022;14(7):1326. Published 2022 Mar 22. doi:10.3390/nu14071326
- Dudenhausen JW, Maier RF. Perinatal problems in multiple births. Dtsch Arztebl Int. 2010;107(38):663-668. doi:10.3238/arztebl.2010.0663
- Schram CA. Outdated approach to a common problem. Can Fam Physician. 2016;62(9):713-716.