It is challenging to meet a woman with vaginal bleeding early in pregnancy and to find a skillful way to explain the fact that they may be having a miscarriage. The following data can help with those conversations:

• About 1/10 pregnancies end up in a miscarriage
• 80% of theses occur in the 1st trimester.  
• 50% of 1st trimester miscarriages occur because of chromosomal abnormalities.
• The risk for a a miscarriage goes up with maternal age—starting at about 10% for mothers in their early 20’s to 80% for mothers who are 45 years old.

Diagnosing Miscarriages

It is important to have guidelines to rely on so that we don’t tell someone they are miscarrying if they actually have a viable pregnancy.

Straight Forward Cases for diagnosing a miscarriage:

• Vaginal bleeding and a prior US showing an IUP, with repeat US with an empty uterus.

Other than that clear situation, there are criteria that can be used with a single ultrasound and other criteria that require serial scans.

On the INITIAL SCAN you can diagnose a miscarriage in the following situations:

• Big sac with no fetus: mean gestational sac diameter ≥25 mm with an empty sac
• Big enough fetus with no HR: embryo with crown-rump length ≥7 mm without visible embryonic cardiac activity
• It’s been a long time and the sac is still empty: 70 days of gestation and a mean gestational sac diameter ≥18 mm with no embryo
• It’s been a long time and the fetus is still small with no HR: 70 days of gestation and embryo with crown-rump length ≥3 mm without visible heart activity

 
For all other situations you need to have at least two scans to diagnose a miscarriage. The second scan is typically one week later.  The criteria for diagnosing a miscarriage on serial scans:

• Both scans with no fetal HR: initial scan and repeat scan after at least seven days with an embryo without visible heart activity
• The sac does not grow enough: pregnancies without an embryo and mean gestational sac diameter <12 mm where the mean diameter has not doubled after 14 days or more
• You give it time and the fetus does not show up: pregnancies without an embryo and
• mean gestational sac diameter ≥12 mm showing no embryonic heartbeat after seven days or more

A couple of other initial scan findings that increase the risk of miscarriage but are not diagnostic and require a repeat US in 7-14 days.

• Slow fetal heart rate: less than 100 beats per minute at 5–7 weeks of gestation
• Subchorionic hemorrhage.

Finally, what do you do when you diagnose a miscarriage. There are three options: Expectant management, medical management and surgical management. This should be guided with the help of a gynecological consult.

• Expectant management: successful for around 80% of women.  This is only an option in the 1st trimester and it can take up to 8 weeks to complete (which is surprisingly long).
• Medical management: typically done with misoprostol. It reduces the need for surgical treatment by about 60%. It can be a one does treatment, but if the first does is not successful a second dose is usually tried.  
• For both expectant and medical management it is important to give guidelines for how much bleeding is too much bleeding. Generally soaking two pads/hour for 2 consecutive hours is considered dangerous bleeding and is the trigger for when the patient should return to the ER.
• Surgical management: for any woman with signs of infection, significant hemorrhage or hemodynamic instability. Also used when medical or expectant management is not successful.

Loss EP. Pb150-2. Am Coll Obstet Gynecol Pract Bull No 150. 2017.

Preisler J, Kopeika J, Ismail L, et al. Defining safe criteria to diagnose miscarriage: prospective observational multicentre study. BMJ. 2015;351:h4579.