Week 4 of pregnancy is the first point in which a pregnancy test will be positive. This is true for a blood or urine pregnancy tests. Pregnancy tests measure a hormone called HCG and it is not until week 4 that HCG is being produced. Checking a urine pregnancy test with the first urine of the morning is the most accurate because that is when the amount of HCG is highest in the urine.
Pregnancies are dated using the first day of the last menstrual period. This means that by convention pregnancy is considered 2 weeks at the time of conception. Week 4 of pregnancy is 4 weeks after the first day of the last menstrual period but only 2 weeks from conception. It takes some time for the fertilized egg to move down the fallopian tube and then implant into the uterus. It takes time after implantation for the hormone HCG to accumulate in the blood steam. Week for of pregnancy is about the time a women would expect her monthly period. This is why pregnancy tests can be positive around the time the period is expected.
An ultrasound done during week 4 will appear the same as a non-pregnant ultrasound. The pregnancy is too small to detect on the ultrasound. This nis important to understand if an ultrasound is performed early in pregnancy. Often ultrasounds will need to be repeated in 1-2 weeks after an initial early ultrasound to confirm a normal pregnancy in the uterus.
There are generally no symptoms of pregnancy at 4 weeks. This is because the traditional symptoms of pregnancy such as nausea, breast swelling and tenderness, and fatigue are caused in great part by the pregnancy hormones, especially HCG. Since these hormones are just starting to appear, there are not enough of these hormones in the body to cause symptoms.
Spotting is very common at week 4; this is referred to as “implantation bleeding”. As the embryo implants into the uterus and starts to grow there is often spotting associated with this process. This is not dangerous and is not a warning sign of a miscarriage. Sometimes women mistake this spotting for a menstrual period and that can cause the due date to be confused do to an error in the last menstrual period. This will be adjusted after the first ultrasound. Implantation bleeding id not associated with significant pain although there may be some mild cramping. Bleeding with significant pain is an indication to be seen immediately to make sure it does not represent an ectopic pregnancy.
When you find you have a positive pregnancy test, even if you are very early like in week 4 of pregnancy, you should choose your obstetrician. You can call their office and schedule an appointment so you can start the process of prenatal care. If your pregnancy test is positive, you should refrain from alcohol, tobacco, and drug use. You should also start a prenatal vitamin.