My lining is thin. What does that change?

The endometrium is the lining of the womb, and it is where an embryo implants.

It grows each month in response to oestrogen, then changes under progesterone so an embryo can attach. If it stays thin, implantation is less likely. That is why the lining is measured before an IUI and before every embryo transfer. It is also why a thin lining is a common reason for a transfer to be moved.

A lining under 7 mm is usually called thin; before a frozen transfer, we usually look for a lining over 8 mm.

ESHRE, the European fertility society, uses under 7 mm as its working definition of a thin lining. These are guide numbers, not a pass mark. Pregnancies do happen with thinner linings, and a lining a little under the target with a good pattern may still be used. Beyond an adequate thickness there is no gain from being thicker. An unusually thick lining can itself need a look, for example for a polyp.

By a vaginal ultrasound scan, timed to the point where a decision has to be made.

In a natural or tablet cycle, it is measured in the days before ovulation, during follicle tracking. In a medicated frozen transfer cycle, the scan is usually about 10 days after oestrogen tablets start. The scan also shows the pattern of the lining (a 'triple line' before ovulation is typical) and, if needed, its blood flow. A scan in a natural cycle can also show how your lining grows on its own, which helps after repeated failed transfers.

Usually scarring inside the womb, past infection, or not enough oestrogen reaching it; sometimes no cause is found.

Scarring (adhesions, also called Asherman syndrome) can follow a D&C, a surgical evacuation after miscarriage, or surgery on the womb. Infection can also scar the lining; genital tuberculosis is one cause still seen in India. Low oestrogen, from irregular ovulation or from some ovulation medicines, can leave the lining under-grown. Poor blood flow to the womb plays a part in some women. In PCOS, the lining is more often thick than thin, so a thin lining in PCOS needs its own check.

Often, yes, when the cause is found and treated; treating the number alone rarely works.

If scarring is suspected, a hysteroscopy (a thin camera through the cervix) can see it and release it in the same sitting. Infection is treated. Oestrogen can be given at a different dose, by a different route, or for longer. If the lining is still thin, the embryos stay frozen and the lining is prepared again in a later cycle. Repeating an identical cycle rarely gives a different result. [CONFIRM: Jananam's usual order of steps]

Sometimes waiting is the better choice, because a frozen embryo can wait safely while the lining is prepared again.

Your doctor weighs the measurement, the pattern, how the lining grew, and how many embryos you have. A thin lining on one scan may just need more days of oestrogen. Most transfers at Jananam are frozen, partly so the lining can be prepared under calmer conditions than during stimulation. A lining that looks fine is not proof it is ready. Tests that claim to time the 'window' of the lining exist; Dr Vani's own experience with one of them is below.