Fast Facts About Gender Selection



  • Gender selection is also widely known as sex selection, with the two terms being used exchangeably. It may also be referred to as family balancing as some people choose to do it to have a child of specific sex after having many children of the other.
  • There are two main methods of gender selection though only one is widely accepted and used by the reproductive medical community today. Other alternative theories involve diet and other modalities, though these have no scientific backing and should not be taken seriously until proven.
  • Sex selection is possible because males and females have different sex chromosome combinations, females have an XX chromosome pair, and males have an XY chromosome. Being able to selectively choose sperm that contain a desired X or Y chromosome or embryos containing either XX or XY chromosome pairs enables one to select the sex of their child.
  • Gender selection is not a stand-alone service. The preferred method of sex selection involves In Vitro Fertilization (IVF) in conjunction with Preimplantation Genetic Testing (embryonic testing – also known as PGS or PGD).

How Does Gender Selection Work?

The sex or gender of the baby is determined by two chromosomes known collectively as the Sex Chromosomes.  Egg cells from the female always carry an X chromosome while male sperm carries either an X or a Y chromosome. If a sperm with an X chromosome meets the mother’s egg, then the resulting embryo and baby will be a girl with an XX chromosome. If a sperm with a Y chromosome fertilizes the woman’s egg cell, the resulting child will be a boy with an XY chromosome.

As you likely already know, there is a pretty much even 50/50 split between boys and girls conceived naturally. Thus, to confidently determine the sex of your future child, you must be able to accurately select a sperm that contains a Y Chromosome or an embryo with XY chromosomes.

Detailed Steps of IVF Gender Selection

Because accurate gender selection requires In Vitro Fertilization, which in and of itself is a fairly intensive process, it’s essential to understand at least at a basic level what the whole process will entail. In general, IVF has four main steps:

  • Ovarian Stimulation: The woman takes hormone-based medications to make such high quality, fully developed eggs (as opposed to the one that is usually made).
  • Egg Retrieval: Removes the eggs from the ovaries.
  • The Embryology Laboratory: Fertilization of the eggs, embryo development for 3-7 days.
  • Embryo Transfer: An embryo transfer is a process of putting an embryo back into the intended parent’s uterus.

Because gender selection requires additional embryonic testing (which takes several days to get the results from), it not only requires additional steps specific to the testing of the embryos, but it requires two “treatment cycles.” One involves the making and testing of the embryos, and the other, a Frozen Embryo Transfer Cycle involves the preparation of the uterus for transfer and the FET itself.

Embryo Freezing



Briefly, embryo freezing is a procedure that adapts to the developmental stage of the embryo. Embryos are placed in prepared media designed to protect embryos from extremely low temperatures. An instrument, controlled by a computer, slowly reduces the temperature of the solution until it reaches –80C Embryos are then labelled and stored individually in tanks filled with Liquid Nitrogen which maintains a temperature of –196C. No biological activity can be observed at these temperatures, and embryos can be stored until the patient is ready for them to be thawed. The freeze-thaw procedure yields a 20% loss of vitality, and those embryos that survive have a subsequent 1/3 chance of implantation compared with fresh embryos. Technology, however, is continually improving survival rates. Technically, frozen embryos can be stored indefinitely depending on the couple’s decision. Although conventionally, embryos are stored for a maximum of 3-5 years, case reports show that embryos can be stored for extended periods. By having couples renew their contract yearly, they can decide whether they want to thaw and transfer the embryos back to the uterus, destroy them or donate the embryos to research.

If there are excess good quality embryos after embryo transfer, these can be frozen and stored. Even though not all embryos will survive the freeze-thaw procedure, pregnancy rates have approached fresh embryo transfers. Embryo freezing has become an established method and has been practised for nearly 20 years, particularly in situations where many oocytes have been retrieved—freezing after embryo formation has provided a second chance for couples whose first attempt did not result in pregnancy. Preparation of the patient for a thawed embryo transfer is medically simpler and less intrusive. In some cases, patients come back to transfer the stored embryos to conceive a second child.

Embryos can be frozen at any point during their development. One can see fertilised eggs on the first day, and then the zygote begins dividing to become an embryo. On the 5th day, the embryo becomes a blastocyst, a stage that shows better results after the freeze/thaw procedure.

The Health Ministry in our country has extended the duration of embryo storage to 5 years. Electronic records where only authorised people with a password can access are made of each patient file. These records have five backups made daily and stored in different places. Two copies are stored in another building for safety in the event of the destruction of the whole building, such as fire, earthquake etc.


This is a method where embryos are frozen quickly to prevent ice crystal formation. When the solution freezes, it solidifies to form a glass-like appearance. This procedure aims to avoid ice crystal formation inside the cell while the temperature is reduced. DMSO (DimethylSulfoxide) and Ethylene Glycol are the most commonly used cryoprotectants. After the embryos are labelled, they are plunged directly into Liquid Nitrogen. Currently, vitrification has become more popularly used in most IVF clinics as the method has shown better survival rates and pregnancy rates than the slow freezing process.

Sperm Freezing



If the male has to have radiotherapy and/or chemotherapy, this can lead to infertility. In some cases, if the husband cannot be present on the day, his partner’s eggs are collected for various reasons, such as a business trip or psychological reasons. In such cases, sperm can be frozen in advance and stored. Unlike freezing embryos and oocytes, survival rates of sperm after freezing and thawing are high. Pregnancy rates following sperm freezing and thawing are close to those of fresh sperm.

Egg (oocyte) Freezing



Oocytes (eggs) that are retrieved from the patient can be frozen and stored irrelevant to the maturation stage. Unfortunately, this method does not yield high pregnancy rates. Lately, however, vitrification has been a more successful method for freezing eggs. This method can be applied to women who undergo chemotherapy or do not have a partner and want to delay motherhood.

Who are Embryo Donors?



There are three types of embryo sources.


  1. Donor oocytes are fertilised with donor sperm, and the resulting embryos are transferred to the recipient’s uterus. This method has high success results.


  1. People in the donor program may want to donate excess embryos and have the recipient family share the costs. If this is arranged before the procedure, fresh embryos can also be transferred to the recipient.


  1. Couples who have excess frozen embryos resulting from IVF treatment, in general, may want to donate their embryos. Frozen embryos will be used in this situation, and because the freezing process compromises the embryos’ vitality, chances of pregnancy are lower than usual.


Criteria established for sperm and oocyte donation applies to embryo donation. The male should be between 18-60 years old, and the woman should be 18-34 years old. The donor family should show that they do not have a genetic or an infectious disease. Only the best quality embryos before freezing should be used as donor embryos.



Preparation of the recipient for donor embryo transfer:

The embryos are transferred when the endometrium is deemed ready through ultrasound examination. Preliminary tests done on the embryo recipient are similar to those of the oocyte recipient. Hysteroscopy might be necessary for the clinicians to view the endometrium in detail. Endometrial thickness is monitored through vaginal ultrasonography, and to achieve the best pregnancy rates, the endometrium should be at least 8mm. If the recipient menstruates regularly, the endometrium is prepared during a natural cycle or after suppressing menstruation using hormones. The recipient continues taking estrogen and Progesterone after the embryo transfer. If she does become pregnant, she will continue taking the hormones; if the pregnancy test is negative, she stops using the drugs, and even if she is menopausal, she will have menstrual bleeding within the week.

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