Checking on progress

The morning after egg collection the embryologist checks the eggs carefully under a microscope for signs of fertilisation. The embryologist hopes to see two pronuclei (PN) inside each egg — one containing the genetic material from the egg and the other containing material from the sperm — because this indicates that the egg has been fertilised normally. About 5 per cent of fertilised eggs are abnormal, in most cases because more than one sperm has been 'let in' so that there are three or more pronuclei instead of two. Figure 7-2 shows a normally fertilised egg with its zona pellucida (egg shell), polar bodies (the material that the egg gets rid of as part of the maturation process in preparation for the 23 chromosomes that the sperm brings) and its two pronuclei (a 2PN embryo).

In some clinics the embryologists check the eggs a second time the day after egg collection to assess the speed of early embryo development, as this gives them an idea of the embryos' potential to develop into an ongoing pregnancy.

On day two after egg collection the embryologist checks the eggs again under the microscope. By now the eggs should have started to divide and form cleavage stage embryos (see the sidebar 'Embryo development'). The embryologist studies each embryo's in detail, looking for the following:

i Fragmentation: Sometimes bits of an embryo's blastomeres break off and cause embryo fragmentation (broken pieces in the embryo). The less fragmentation the better, but only about 20 per cent of embryos have no fragments whatsoever.

i Number of blastomeres: On day two after egg collection the embryo should have three to six blastomeres.

i Shape of blastomeres: The blastomeres should have a spherical shape.

i Size of blastomeres: Ideally, the blastomeres should be of even size.

i Zona pellucida (egg shell): This should be intact with no 'cracks'.

Figure 7-2:

A 2PN embryo.

Male pronucleus

Female pronucleus

Embryo development

Embryos develop by cell division. Initially, the egg and sperm form a single cell, which has the genetic material of the mother and the father. This cell divides and forms two identical cells. These two cells then divide to form four cells and so on. The early embryo is called a cleavage stage embryo and the cells are called blastomeres. The daily increase in the number of blastomeres indicates how healthy the embryo is: Three days after egg collection an embryo is expected to have between six and 12 blastomeres. Depending on the clinic's practice, one or two of your embryos are transferred to your uterus two to five days after egg collection.

The embryologist grades the embryos according to their looks. The grading scheme describes the quality of the embryos and their potential to continue to develop after embryo transfer. Information about the quality of the embryos that are transferred allows your doctor to estimate your chance of pregnancy. Clinics vary in the grading systems they use to classify embryo quality, but the best-quality embryos have the greatest chance of developing into babies. These embryos have the expected number of blastomeres, which are even-sized and spherical in shape, no or very few fragments and an intact zona pellucida. In poor-quality embryos more than half the blastomeres are fragmented, and the blastomeres don't all have the same shape or size. Embryos may also be classified as nonviable, which means that they have no intact cells: Such embryos have no chance of continuing their development. Figure 7-3 shows the difference between a four-cell embryo and a fragmented embryo.

Figure 7-3:

The difference between (a) a four-cell embryo and (b) a fragmented embryo.

Figure 7-3:

The difference between (a) a four-cell embryo and (b) a fragmented embryo.

Pregnancy Diet Plan

Pregnancy Diet Plan

The first trimester is very important for the mother and the baby. For most women it is common to find out about their pregnancy after they have missed their menstrual cycle. Since, not all women note their menstrual cycle and dates of intercourse, it may cause slight confusion about the exact date of conception. That is why most women find out that they are pregnant only after one month of pregnancy.

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