We have all done it: we are talking with our friends or family about kids, and at one point admit ‘I am ONLY having boys’ or ‘If I don’t have a girl, I don’t know what kind of parent I’ll be!’ This banter is often light-hearted, and some couples are determined to have a baby of the sex that they choose. The concept of preconception sex selection brings many ethical dilemmas to light, which we will get to later. For now, let’s talk about the reality of what determines baby’s sex, and then move into current theories around how to select baby’s sex prior to conception.
Quick anatomy and physiology lesson on reproduction: a human’s sex is determined by the two sex chromosomes they receive at conception. Every egg cell (mom) carries an X-chromosome, and sperm cells (dad) can carry either X- or Y-chromosomes. When the sperm and egg unite, the combined chromosomes determine the sex of the new embryo. Girls will have two X chromosomes (XX), and boys will have one X and one Y chromosome (XY).[Note: there are some genetic diseases in which an additional sex chromosome is present; however, information regarding those conditions is outside of the scope of this article].
To be honest, the chance of just conceiving is rare in itself; the chances of conceiving a particular sex, cuts that number in half. It has been shown that couples who have sex during the woman’s fertile window have a 25% chance of getting pregnant.1 Add in the fact that there is a 50% chance of conceiving one gender over the other, and the chance of conceiving a boy (for example) during a woman’s fertile window is 12.5%. As we move forward, there will be many options presented that are backed by little to no scientific evidence. The most important thing to keep in mind is you and your potential future baby’s health and safety. Some of these theories can be dangerous for particular populations, and you are strongly encouraged to speak with your primary care provider before pursuing any drastic lifestyle changes.
Assistive Reproduction Technology
Now that you have been sobered into having a critical eye for conception information, let’s get into the medical technology that is out there. There are currently two major technologies out there: IVF + PGD and sperm sorting.
IVF + PGD is Invitro Fertilization plus Preimplantation Genetic Diagnosis. Basically, the mother is given medication to cause the maturation of multiple ova, which are then extracted and combined with sperm of the father or a sperm donor in a petri dish. After the embryos start to develop, a biopsy is performed to diagnose any genetic disorders, and the couple can choose which embryo(s) are implanted into the wall of her uterus. During the biopsy phase is when the sex of the embryo is discovered.2
Right now, this technology is primarily used to avoid passing on sex-linked genetic diseases. For example, Duchenne muscular dystrophy is typically passed down boys due to their only having one X chromosome. However, some clinics will allow couples to use the treatment for sex selection or “family balancing.” 2
Sperm sorting is exactly what it sounds like: take some sperm from the father or a donor, sort out which ones are carrying X’s and which ones are carrying Y’s, and then implant the desired group into the mother’s uterus via intrauterine insemination (IUI) or can be combined with IVF alone or IVF + PGD. 2 There are two current methods:
MicroSort®: Currently only available in Mexico, North Cyprus, Malaysia, and Switzerland, this technology uses a dye that picks up genetic information to sort. X-chromosomes contain more genetic information than Y-chromosomes, so they show up more brightly, and the sperm are sorted one by one. 2 Here’s some data:
- For couples who wanted a girl, the “female” sperm samples contained 87% X-chromosome-carrying sperm. When used with IUI or IVF, and when a successful conception, pregnancy, and birth were achieved, 93% of couples had a baby girl. 2
- For couples who wanted a boy, the “male” sperm samples contained 74% Y-chromosome-carrying sperm. When used with IUI or IVF, and when a successful conception, pregnancy, and birth were achieved, 85% of couples had a baby boy. 2
Ericsson Albumin Method: This method is more widely available, although it remains controversial because it is based on the theory that Y-chromosome-carrying sperm are lighter and can swim faster than X-chromosome-carrying sperm. This theory has recently been disproven: all sperm are capable of swimming at the same speed regardless of chromosome. That being said, the Ericsson Albumin Method places carefully washed sperm into a layered albumin solution that is denser on the bottom. The assumption is that the Y-carrying sperm will swim faster and reach the bottom layer sooner than the X-carrying sperm. From there, the sperm can be sorted and implanted accordingly. 2 Here’s the data:
- Approximately 80% of couples conceived boys as planned2
- A little over 70% of couples conceived girls as planned2
- Between 15-30% of babies born with this method will not be the sex the parents hoped for2
This section is for the theories developed by doctors that still lack evidence of their effectiveness: Shettles and Whelan.
Shettles: This theory was developed in the 1950s, when the belief was that Y-carrying sperm were smaller, faster, and more ‘fragile’ than X-carrying sperm. Dr. Landrum Shettles suggests these techniques to naturally conceive a boy:
- Deep penetration. Give the Y-carrying sperm a head start by choosing positions during intercourse that allow for deeper penetration.2,3 Known positions are “doggy-style,” standing, and straddling.3
- Cycle timing. Because Y-carrying sperm was thought to be faster and less resilient, Shettles proposed having intercourse as close to peak ovulation as possible. There are many ways to track ovulation including basal body temperature, vaginal mucous tracking, and using an ovulatory predictor kit.
- Dad’s undies. Tighter underwear holds the scrotum closer to the body, which increases the temperature during sperm production. Due to the idea that Y-carrying sperm were less resilient/more fragile, it was assumed best not to overheat them.2,3
- Come on, girl! According to Shettles, when the mother orgasms an alkaline solution is released in the vagina that creates an ideal environment for sperm. Y-carrying sperm in particular are thought to do better in more alkaline environments, while X-carrying sperm can tolerate slightly more acidity.1,2,3
Whelan2: Dr. Elizabeth Whelan was an epidemiologist who came up with this theory based on the 1970s research of Dr. Rodrigo Guerrero. Her method was the exact opposite of Shettles’ suggested timing: she suggested having intercourse many days before ovulation to conceive a boy, or having intercourse close to or on the day of peak ovulation to conceive a girl.2FINAL THOUGHTS: With both of these techniques, choosing an even smaller window of time to have intercourse decreases overall chances of getting pregnant at all based purely on the fact that less intercourse is happening. There is also no data to conclusively support one theory over another.
When looking at the dietary impact on baby’s sex, researchers have latched onto three major areas: caloric intake, dietary pH, and mineral intake. Again, there is limited to no evidence on any of these ideas.
Caloric Intake: It is thought that women who have a higher caloric intake, particularly with a high fat content, are more likely to conceive a boy. 1,2 This one is highly unlikely, as the original research on sex ratios in time of war and famine has been disproven with more recent studies. 2
Dietary pH: Leading from Shettles’ idea of maintaining an alkaline environment for Y-carrying sperm, it is thought that diets containing more alkaline foods would increase chances of conceiving a boy, whereas diets that contain more acidic foods would increase the chances of conceiving a girl.1,2 Again, there are gaps in the research. We know that X-carrying sperm can tolerate more acidic environments due to petri-dish studies; 2 what we do not know is how much a woman’s diet really affects her vaginal pH. The body has developed amazing mechanisms to maintain homeostasis, particularly for pH. It is unlikely that eating more beets will alter those mechanisms enough to make a significant change.
Mineral Intake: The rules around this one are more sodium and potassium and less calcium and magnesium will increase chances of a boy, and less sodium and potassium and more calcium and magnesium will increase chances of girl.1,2 One study found that 81% couples who wanted a girl and regulated their timing and participated in intentional supplementation ended up conceiving and giving birth to baby girls. Do not be deceived though; this study had a HIGH (78%) drop-out rate, and no other evidence corroborates their findings.2FINAL THOUGHTS: Again, it is up in the air. The most important thing is to talk to your primary care provider or a dietician before implementing any drastic dietary changes. Some proposed diets have dangerous risks if implemented for a long period of time, and people who have had prior eating disorders may relapse. I cannot stress enough: talk to your doctor!!
Considerations for Preconception Sex Selection
It is clear that there are a lot of options when it comes to preconception sex selection; not all are valid, and NONE are guaranteed. Choosing to build a family is a big decision and can seem daunting because we know that we are not in control of every aspect of it. There are plenty of reasons why parents may want to have a child of one sex or the other, some are medical, and some are non-medical. Medical reasons come into play with sex-linked genetic disorders; couples may opt for a girl to avoid passing on a disease that would affect a boy and vice versa. In this situation, assistive reproductive technology is more accessible to parents. Non-medical reasons include preference, cultural or religious beliefs, and/or death of a child.
It is also important to consider both personal and larger impacts of preconception sex selection. I mentioned the ethical dilemma with the un-implanted embryos from IVF, and parents may also struggle with unconditional love for their child if they do not end up conceiving the desired sex. There are also cultural and religious practices to consider both with preferential sex and with interfering with God’s plan. As citizens of our world, we are required to reflect on the larger impact of our decisions. One of the largest concerns around preconception sex selection is the lean toward eugenics, or ‘designer babies,’ which would enable parents to construct their offspring. There is also the concern of societal well-being, and the consequences of having disproportionate numbers of each sex.
Everyone has at one time or another had a sex preference for their children; it is normal, and nothing to be ashamed of. In the end of the day, a baby is conceived and born, and parents fall in love; once that bundle of joy arrives, the sex just doesn’t seem to matter anymore. There have been technological advancements that can allow us to know more about our children sooner, however they are not readily accessible and are very expensive. Other “natural” methods remain to be proven. Most are harmless and talking to your primary care provider will help with mitigating risks and having a healthy pregnancy.