The Process of Implantation and IVF Success

 Implantation is referred to the stage of pregnancy at which the embryo adheres to the wall of the uterus. It helps the embryo to grow by receiving nutrients from the mother.

In humans, implantation of a fertilised ovum is most likely to occur around 6 – 9 days after ovulation. The reception-ready phase of the endometrium of the uterus is usually termed the “implantation window” and lasts about 4 days.

The term “implantation” is used to describe process of attachment and invasion of the uterus endometrium by the blastocyst (conceptus).

Implantation is a highly co-ordinated event that involves both embryonic and maternal active participation.

Initially the newly hatched blastocyst loosely adheres to the endometrial epithelium. Then it rolls over the endometrium to find a suitable place for implantation where it gets attached firmly.


What happens in implantation window?

Embryo–endometrial dialogue has led to the identification of a ‘window of implantation’. The implantation window is characterised by changes to the endometrium cells, which aid in the absorption of the uterine fluid. These changes bring the blastocyst nearer to the endometrium and immobilise it. The first step of implantation is the formation of foetal–maternal interface. Next crucial step is invasion of the embryo into the endometrium.

How implantation is mediated?

 Implantation is initiated when the blastocyst comes into contact with the uterine wall. Certain molecules and pinopodes are involved in bringing embryo and endometrium together and attachment in embryo implantation. The embryo produces cytokines and growth factors and receptors for endometrial signals.

Does body immunity play role in successful pregnancy?

The embryo, as a genetic product of both maternal and paternal chromosomal material, can be seen as an allograft to the uterus. The body immune system plays an important role in implantation process. The host (mother)genetically different from the transplants(foetus), raises the possibility of a graft-versus-host reaction. The immunological action against the embryo can be described as maternal restraint.

Can we calculate Implantation period?

Implantation of a fertilized ovum is most likely to occur around 6 – 9 days after ovulation. It falls around day 21 of a regular menstruation cycle. In irregular cycles, it is difficult to predict. During the female fertile age, there is an average chance of pregnancy of approximately 15% per cycle.

Does implantation process differ in IVF and natural pregnancy?

 The assisted reproduction setting for implantation is not different to a naturally conceived pregnancy.

But at times, during IVF treatment, the factors for implantation may be adversely affected. This is attributed to high level of steroid hormones and drugs used for pituitary desensitization. Imbalance in the oestrogen and progesterone interaction may result in implantation failure in a number of patients.

Can we enhance implantation by PGD?

Embryonic factors are by far the main factors determining whether or not a successful implantation and pregnancy will occur.

PGD seems to be a safe procedure that can enhance pregnancy rates by improving embryo quality by selection. Preimplantation genetic screening (PGS) enables the testing of gametes and embryos for numerical chromosomal aberrations commonly found in early pregnancy loss.

What are the early signs of implantation?

Embryonic implantation is the establishment of pregnancy, to be proven by finding human chorionic gonadotrophin (HCG) in maternal blood. Some women may experience slight bleeding and cramping pain during the process of implantation.

 What is the role of embryo transfer procedure in implantation?

The performance of an atraumatic embryo transfer is essential to implantation and IVF success. Factors such as the contamination of the catheter tip with cervical bacteria, stimulation of uterine contractions during the procedure, may significantly influence implantation rates. Usually embryo transfer is performed under ultrasound guidance by use of soft catheters for better success.

 What is recurrent implantation failure?

Recurrent implantation failure is an important cause of repeated IVF failure. It is estimated that approximately 10% of women seeking IVF treatment will experience this particular problem. It is a distressing condition for patients and frustrating for clinicians and scientists. Recurrent implantation failure refers to failure to achieve a clinical pregnancy after transfer of at least four good-quality embryos in a minimum of three fresh or frozen cycles in a woman under the age of 40 years. The failure to implant may be a consequence of embryo or uterine factors.