Sperm-Binding Beads Can Work as Either Contraceptive or Fertility Aid

Women typically release just a single egg when they ovulate, although men release tens or even hundreds of millions of sperm every time they ejaculate. The chemical that enables just one sperm to become the partner of the available egg is being harnessed both to enable pregnancy and to prevent it.

Dr. Jurrien Dean and his colleagues at National Institute of Diabetes and Digestive and Kidney Diseases in Bethesda, Maryland, have developed a technique of manufacturing tiny plastic beads that emulate the shape and size of a human egg. To these beads they have applied a protein called ZP2. This is the same protein that sperm recognize when they bind to an egg to fertilize it.

Selecting the Best Sperm for In Vitro Fertilization (IVF)

While sperm use ZP2 as a kind of navigational aid to find the egg, they aren't bound to ZP2 as if it were some kind of glue. A sperm that binds to a plastic bead coated with the protein can release itself when it recognizes that the plastic bead is not a human egg. This ability makes the protein-coated bead system helpful in in vitro fertilization, also known as IVF. Only the healthiest "swimmers" in a semen sample will attach themselves to ZP2-coated plastic bead right away. Placing the beads in a semen sample allows fertility doctors to collect only the most viable sperm to fertilize an egg harvested for later implantation into a woman with infertility problems seeking to become pregnant.

Also Useful as a Contraceptive

The same property of the ZP2 protein potentially makes it useful as a contraceptive. Dr. Dean and colleagues implanted the protein-coated beads into the uteruses of female mice of reproductive age. Even though the female mice were kept in the same cages as sexually active male mice, they failed to get pregnant even after ten breeding cycles (ten ovulations).

Adapting ZP2 for use in contraceptives for human women will probably take some fine tuning. An implanted bead could potentially only deliver sperm to the egg released from the fallopian tube only that much faster. Probably the system will have to be modified so that the ZP2-coated beads direct sperm to a sponge coated with a spermicide. However, if this method works, women would no longer have to rely on hormone-based methods such as the Pill.

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What's the Problem with Hormone-Based Contraception for Women?

Side effects of birth control pills are uncommon, but they can be unpleasant or even very dangerous. Some women using the Pill experience:

• Breast tenderness.
• Breakthrough bleeding or spotting.
• Slight increases in blood pressure.
• Chloasma, formation of spots on the upper face, mostly over the upper lip, under the eyes, or across the forehead.
• A 200 to 600 percent greater risk of blood clots in the legs (venous thromboembolism).
• Depression, irritability, and mood swings.
• Increased risk of glaucoma.
• Decreased glucose tolerance, and increased risk of diabetes.
• Greater risk for glaucoma.
• Certain nutrient deficiencies, especially vitamins B2, B6, B12, and C, folic acid, magnesium, selenium, and zinc.
• Weight gain, especially with high-progesterone versions of the Pill. Of course, pregnancy is a sure-fire way of gaining weight.

Add to these problems, the Pill has to be taken on an exact schedule. Taking the Pill on the wrong days of a woman's menstrual cycle can leave her at risk of pregnancy.

Why Hormone-Based Contraception Sometimes Kills a Woman's Interest in Sex

The Pill has the advantage of being reversible. When women stop taking it, they tend to get pregnant. Women can choose to become mothers when they are ready. About half of women get pregnant within three months of stopping the Pill. Most women get pregnant within one year of stopping oral contraceptives. 

However, the Pill has one other effect that isn't as often mentioned. It sometimes kills a woman's interest in sex.

Some Women Report a Higher Sex Drive on the Pill, Some Lower, and Some the Same

Using the Pill doesn't always interfere with a woman's love life. Some women report an actually stronger libido when they are on the Pill. Others report no change in their interest in sex. An review of 36 clinical studies of this question reported in 2013 in the European Journal of Contraception and Reproductive Health Care found that only about 15 percent of women lose their sex drive when they are on the Pill. However, losing interest in sex cancels out the main benefit of taking the Pill, having more sex with fewer consequences.

Testosterone Explains Why Some Women Lose Interest in Sex When They Are on the Pill

The reason some women lose interest in sex when they are on the Pill has to do with their testosterone levels. Women's bodies make small amounts of testosterone that power their interest in sex. This testosterone is made in the ovaries. The ring, the patch, the shot, or the implant for contraception shut down ovulation from the ovaries, but they also slow down the production of testosterone in the ovaries.

Additionally, the estrogen in birth control increases the production of sex hormone-binding globulin (SHBG). This protein binds to testosterone so that it is not as readily available to fuel the sex drive. A study in the Journal of Sexual Medicine in 2006 found that women who are on the Pill produce four times as much SHBG as women who are not.

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Women who get "horny" about the time they ovulate experience increased sex drive because the ovaries release testosterone about the same time they release an egg to be fertilized. When the ovaries don't release an egg, due to the contraceptive, they don't release testosterone, either. They also don't get as "wet." They don't produce as much natural lubrication.Women who are used to becoming highly sexual about the midpoint of their menstrual cycles may miss this monthly peak of sexual interest when they go on the Pill.

Certain Kinds of Contraceptive Pill Have More of an Effect on Sex Drive Than Others

High-estrogen versions of the Pill have fallen out of favor, but it's high-progesterone versions of the Pill that have the greatest effect on sex drive. Different versions of synthetic progrestin have different effects on a woman's interest in sex. Yaz and Yasmin contain a form of progestin called drospirenone. It is very anti-testosterone. It will clear up acne but wipe out sex drive. Lutera and Lybrel contain another form of progestin called levonorgestrel. It behaves similarly to testosterone and may actually increase sex drive.

A truly effective contraceptive sponge, however, will help women avoid all the side effects associated with the Pill, as well as give them the ability to try to get pregnant any time they like. In the meantime, the hormone-free copper IUD may be the next best thing.