Implantation bleeding: what it is and when spotting needs checking

After fertilisation the developing embryo plants itself in the lining of the womb. Tommy's says this usually happens around the time your period would have been due, and that an implantation bleed is very light bleeding (spotting). The NHS signs-of-pregnancy page describes a bleed similar to a very light period, with some spotting or only a little blood, around the time your period is due, and calls this implantation bleeding.

Because it can coincide with when a period is expected, it may be mistaken for a light period, which is one reason a pregnancy test and clinical advice matter if you think you might be pregnant.

Tommy's midwives define spotting as a spot or smudge on wiping, or a stain on pants, that comes and goes rather than being constant, and which can be red, pink or brown. Light bleeding, by contrast, stains a pad or pants and is more constant. An implantation bleed, Tommy's says, should be spotting and not heavy enough to soak through pads or underwear.

The NHS lists a number of other early signs that may be present alongside it, including a missed period, feeling sick, tiredness, tender breasts, needing to pee more often, a metallic taste, and mood changes. Those signs do not confirm a pregnancy; the NHS says a pregnancy test is how you check.

Tommy's lists reasons for light bleeding or spotting in the first 12 weeks: implantation bleeding, subchorionic haematomas, changes to the cervix, vaginal infections, miscarriage, and ectopic or molar pregnancy. It explains that the cervix gets an increased blood supply and becomes softer in early pregnancy, so some bleeding after sex can occur, usually nothing to worry about but worth telling your midwife.

The NHS adds causes such as a urine or sexually transmitted infection and problems with the placenta, and says sometimes no cause is found. Because implantation bleeding is diagnosed mainly by exclusion, a clinician will want to consider the other possibilities, especially if there is pain.

Tommy's advice is to contact your GP surgery, a walk-in service, your nearest early pregnancy unit if it offers self-referral, or NHS 111 for any bleeding with or without stomach pain, and to call NHS 111 or go to A&E if bleeding is heavy, pain is severe or you feel generally unwell. The NHS says to call 999 if you are pregnant and bleeding and have severe tummy pain, pain in the shoulder, feel sick, faint or dizzy, or the bleeding is heavy. Tommy's lists tummy pain on one side, shoulder-tip pain and discomfort when peeing or pooing as ectopic pregnancy symptoms that need prompt advice.

The RCOG says bleeding and/or pain in early pregnancy is common and does not always mean there is a problem, and that you should seek medical advice. Local early pregnancy services vary by area and UK nation.

The RCOG says you may be asked about symptoms and your last period, have a urine pregnancy test, an ultrasound scan, a vaginal examination and blood tests. Tommy's adds that a heartbeat is unlikely to be seen before around 6 to 7 weeks, so the first scan may be about confirming the pregnancy is in the womb, and a repeat scan may be offered after 1 to 2 weeks. A clinician may be able to say after tests whether the bleeding is likely to be implantation or something else, but cannot always do so.