The pregnancy hormone – human chorionic gonadotropin hormone or hCG for short is produced by the trophoblast cells surrounding a growing embryo which will eventually become the placenta. It is this hormone that is measured in urine pregnancy tests. If you have undergone IVF your clinic may ask you to come back for a blood test that also measures the same hormone.
A confirmed pregnancy requires a level of 5 mIU/ml in the early stages and very low levels of hCG can only be picked up in a blood test. But 5mIU/ml is considered a boarder-line result, clinics are usually looking for a level of about 50 mIU/ml to confirm an established pregnancy and if levels are lower, a repeat test is required 2 days later. This is because the hCG levels vary greatly and are dependent on the time of implantation, which nobody knows. Typically, levels should double approximately every 2-3 days.
Over the counter pregnancy tests are not quite as sensitive as blood tests but pretty close and many fertility clinics are happy to rely on a urine test kit rather than a blood test. There are a vast array of pregnancy test kits for purchase now, all offering different ways to display pregnancy, they are all using this same hormone but the sensitivity is different. The pregnancy test kits fall into two categories; early detection – 5 days before the day your period is expected, and those designed to be used on day of period or after. The later are usually a bit cheaper.
The most sensitive test for a 5 day before period test is still First Response. They were first to the market decades ago and their tests will detect hCG at 6.3 mIU/ml. compared to most of the others brands such as Clearblue Ultra Early and Conceive Plus at 10mIU/ml.
One of the most useful tests on the market is Clearblue – with weeks indicator. The test shows how many weeks have lapsed since conception, which is really useful if you are unsure when you ovulated. It uses two hCG measurement strips – one which is highly sensitive and measures low hCG and one with low sensitivity which measures higher hCG. With this test the hCG hormone has to reach the threshold as show on the chart to activate the weekly indicator. So to be 2-3 weeks pregnant you would need to have at least 153 mIU/ml of hCG in your urine.
The number of weeks appearing in the window can be confusing, these weeks are dated from the approximate date of conception but your GP counts you pregnancy weeks from the date of your last menstrual period so if you are 2-3 weeks pregnant technically you are 5-6 weeks pregnant.
|Pregnancy Test||Weeks indicator
|Sensitivity/ mIU/ml of hCG|
|First Response – 5 days before day of period||6.3|
|Conceive Plus – 5 days before period is due||10|
|Clearblue Digital – day of period||25|
|Clearblue with weeks indicator||1-2 weeks||10|