Intrauterine Devices (IUDs): The Basics

The Pulse is a good place for you to information concerning a range of issues related to pregnancy, including contraception. Recently, we have discussed oral contraceptives in connection with a range of situations. We have discussed the issue of how contraceptive use may evatually be affected in some US states as a result of the recent Supreme Court of the United States (SCOTUS) decision on abortion, Dobbs versus Jackson Women’s Health Organization. Birth control discussions have included the topic of oral contraceptive side effects, the risk of thrombosis (blood clots) in women taking oral contraceptives, especially in those who sit down for long periods, as well as benefits and uses of oral contraceptives apart from preventing pregnancy. The issue of whether you can get pregnant following unprotected sex during your period has come up and we have even discussed coitus interruptus. This brings us to another contraceptive method that we have yet to discuss, the intrauterine device (IUD), which we’ll explore today.

An IUD is a T-shaped device with a string extending from the long end of the T. An obstetrician inserts the IUD through the cervix and into the uterus so that the arms of the T are deepest, in the fundus side of the uterus (each pointing toward one fallopian tube) and the lower end of the T in the isthmus, with the string sticking out through the cervix. The presence of an IUD causes a handful of effects, including inflammation locally in the lining of the uterus, the endometrium. The effects make it difficult for sperm to survive a trip through the uterus and into the fallopian tube and to fertilize an ovum (egg), either by killing the sperm or rendering them unable to swim. Additionally, the effects on the endometrium are thought to prevent a blastocyst (a 5-6 day-old embryo) from implanting in the unlikely event that an ovum does get fertilized. This second potential mechanism, a kind of backup, bothers some anti-abortion politicians and activists who consider pregnancy to begin at conception (which actually it does not), because they consider anything that stops the early steps leading to pregnancy to be an abortion.

In the wake of Dobbs v Jackson Women’s Health, there has been some speculation and concern that the SCOTUS may review some future case in a way that interferes with the right to contraception by overturning the SCOTUS decision on a 1965 case called Griswold versus Connecticut. That’s because Griswold v Connecticut was decided based on reasoning very similar to the reasoning of Roe versus Wade. This was one of the implications that Associate Justice Clarence Thomas wrote in his concurrence of the majority decision on the Dobbs case. However, even without the anti-abortion movement and SCOTUS turning overtly against all contraception, there may be threats in some US states against the use of IUDs in particular, because of the uncommon scenario of a fertilization occurring despite the presence of an IUD and then the fertilized entity failing to implant on account of that same IUD. Normally about one or two million sperm cells make it into the uterus, yet only about one per ten thousand make it through the uterus, into the correct fallopian and come into contact with the ovum. This means that about 200 sperm cells make it to the ovum on a good day (or a bad day, depending on your perspective). An IUD makes the environment of the uterus very unfriendly to sperm cells, so, at best, the numbers of healthy swimming sperm cells drop dramatically.

There are two categories of IUD, each with its benefits and drawbacks. One kind of IUD is full of the hormone progestin, which gradually leaks out, causing the mucus in the cervix to thicken and the endometrium to thin out. In addition to preventing pregnancy, an hormonal IUD is useful for treating various conditions, such as menorrhagia (heavy menstrual bleeding), menstrual cramping, endometrial hyperplasia (excessive growth of the endometrium), endometriosis, adenomyosis (growth of endometrial tissue into the muscular wall of the uterus, anemia, and uterine fibroids.

The other category of IUD is the copper IUD, which can remain longer in the uterus (up to 10 years) compared with an hormonal IUD, does not carry a risk of blood clots (which hormonal IUDs carry to some extent), but is not used for treatment of bleeding. It actually carries a risk of some bleeding.

David Warmflash
Dr. David Warmflash is a science communicator and physician with a research background in astrobiology and space medicine. He has completed research fellowships at NASA Johnson Space Center, the University of Pennsylvania, and Brandeis University. Since 2002, he has been collaborating with The Planetary Society on experiments helping us to understand the effects of deep space radiation on life forms, and since 2011 has worked nearly full time in medical writing and science journalism. His focus area includes the emergence of new biotechnologies and their impact on biomedicine, public health, and society.

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