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PMS or Pregnant? How to Tell the Difference

Written by Sara Langer

Photography by Photographed by Maria Del Rio

It’s almost “that time of the month” and you’re starting to experience some less than desirable symptoms. You’ve surely felt some of these changes in your body month after month, but this time there’s something different. Wait, could this be, could you be…pregnant? Or is it just PMS? The very early stages of pregnancy can have a similar effect on your body as PMS, leaving many women—especially those trying to get pregnant—confused. In order to learn a little bit more about what our bodies are going through during ovulation and the days that follow, we turned to Dr. Mary Jane Minkin, Clinical Professor of Obstetrics, Gynecology, and Reproductive Science at the Yale Medical School. She shed some light on the causes, similarities, and differences of these symptoms.

Let’s start with the basic physiology and what causes the overlap in PMS and early pregnancy.
“At ovulation, the area from which the egg is released becomes ‘corpus luteum,’ which in turn makes progesterone. Progesterone does a couple of things. It stabilizes the lining of the uterus, creating a nice environment for the fertilized egg to implant itself. Once the egg implants itself into the wall of the uterus, it stimulates the corpus luteum to hang on and keep going and the fertilized egg will start to produce some of its own hormones. If during the time of ovulation a pregnancy is not established, there is a message to the body that the corpus luteum can die, there’s no need for it to hang around, you’re not pregnant. Once this happens the progesterone levels will go down, the lining of the uterus is not stabilized, and you will get your period. Either way, progesterone will be present during the time of ovulation, causing many of the shared symptoms of PMS and pregnancy. Both estrogen and progesterone will be present in a woman’s body. If she does become pregnant, the levels of these hormone will increase, but if she is not, they will go down a bit and rise again around the same time next month. Some of the common symptoms created by progesterone and estrogen are bloating, breast tenderness, diarrhea, dizziness, drowsiness, fluid retention, headache, irritability, muscle pain, nausea, spotting or breakthrough bleeding, stomach pain or cramping, tiredness, and vomiting. Some of these symptoms occur during PMS and some are more specific to pregnancy. If a woman does become pregnant, her body will start producing the hormone hCg, human chorionic gonadotropin, which is made by the implanting embryo. There is no hCg present in a woman who is not pregnant, it is the hormone responsible for the positive pregnancy test. The effects of hCg on a woman’s body is still up for debate, but one of the most common theories is that the presence of hCg can cause nausea, or morning sickness.”

Are there any characteristics a woman can look for in the most common symptoms of PMS and pregnancy, that would help her determine which is causing them?
“There’s not too much of a difference in how a woman feels with these symptoms, whether or not she is PMSing or pregnant. If a woman is experiencing these symptoms and is eager to know whether or not she is pregnant, an early detection home pregnancy test is a good option. The new technology of these tests can often detect pregnancy 5 to 6 days before a missed period, which is really early! Both estrogen and progesterone can cause retention of fluid and tender breasts, both common symptoms of PMS and early pregnancy. When a woman has her period these symptoms dissipate, but if she is in fact pregnant the symptoms may be persistent for some time.”

Does nausea occur with PMS? We’ve heard of women having very severe menstrual cramps along with nausea.
“Yes, some do, but it doesn’t usually occur with PMS. In general this happens when a woman already has her period. The hormone that is responsible for this is prostaglandin, which is produced in the uterus (and other parts of the body). Prostaglandin can cause contraction of muscles that in turn can create cramping and sometimes nausea. When this happens a woman’s period usually shows up, signifying she is not pregnant, so not to be confused with morning sickness, which generally starts around 4-6 weeks. Again, you usually would have had your period by then if you’re not pregnant.”

You mentioned early detection home pregnancy tests. It can be pretty common to get a false negative on a test, especially if you take it early on in your cycle. What about a false positive result?
“There is a very small chance that you would ever get a false positive. It is very easy to get a false negative if you take the test too early and your body has not yet produced enough hCg to be detected. Ovulation can occur at slightly different times during a woman’s cycle, so if she still thinks she may be pregnant after a negative test, wait a few days and test again. But a positive is positive. Again, the tests detect hCg, which only appears when a woman is pregnant.”

What about chemical pregnancies? Can you tell us a little bit about them?
“There’s been an advent over the last 30 years of both urine and blood tests that detect pregnancy so early on that someone may have a positive pregnancy test, because the egg was in fact fertilized and implanted. Unfortunately, this happens and many pregnancies just don’t develop properly, they get to a certain point and the embryo stops dividing and the embryo dies, the pregnancy then does not occur and you get the cleaning out of the lining of the uterus (your period). There are definitely many chemical pregnancies where the woman is in fact pregnant, but the pregnancy is not successful from the very beginning. It is basically a very, very early miscarriage. Again, because of these early detection tests, more women are aware of a chemical pregnancy, where she is in fact pregnant based on an early detection test, but her period then arrives around the normal time. This is very common. Many women won’t test until after a missed period, so they never know that the chemical pregnancy occurred. Being able to test so early and receive a positive only to have your period a few days later can be disappointing and many women may already have an emotional attachment to the pregnancy, so that can be difficult. The good thing about knowing of a chemical pregnancy is that is does show that the woman can in fact get pregnant. Just getting pregnant is an excellent thing, if that’s what you want. It means the egg and sperm successfully fertilized. It shows, for example, there is no blockage of tubes, something that would prevent a women from getting pregnant. In a chemical pregnancy, the egg and sperm did get together, which is a great thing, it just wasn’t the most perfect or healthiest union and the pregnancy didn’t continue. If this happens a few times, when the woman is testing early on, receiving a positive result, but then getting her period soon after, and she is actively trying to get pregnant, she may want to speak with her doctor to try and investigate what’s going on.”

One common symptom of early pregnancy is implantation bleeding, which could be mistaken for a period. How much bleeding is normal? When should a woman be concerned with the bleeding she may be experiencing if she is in fact pregnant?
“It is very common to bleed around the time of implantation, which would be before or around the time of the missed period, which is why it could easily be confused for a normal period. It’s usually fairly light, not heavy bleeding. This is normal, but the woman should certainly report and let her healthcare provider know what’s going on if she knows she is pregnant and there is some blood. That doesn’t mean she should be worried, it’s totally normal, but it’s good for the care team to be aware of. Again, it’s very common. Over a third of women will have some bleeding during their first trimester of pregnancy. Of those women, half of them will go on to have a totally normal pregnancy, the other half will unfortunately end in a miscarriage.”

Are there any symptoms of PMS or early pregnancy that are not shared?
“Irritability is a common symptom of both pregnancy and PMS, but they generally occur at different times. During PMS, a woman is very likely to be a little irritable, but this would likely happen later on in the pregnancy, not around the time of a missed period. Fatigue is another one. It is very normal in the early part of pregnancy, but not as common during PMS. Yes, a woman may feel drained of energy, but I see that more once the period has already arrived.”

What advice can you give women who may be considering getting pregnant?
“If somebody is even thinking about getting pregnant, I always encourage them to start making sure they are getting plenty of folic acid in their diet. A multivitamin with folic acid or even a prenatal vitamin is great—400 micrograms is all you need. Many women will start taking the prenatal vitamins once she finds out she is pregnant. However, it’s even better is she is already taking them when she conceives. Having folic acid on board at the time of ovulation and fertilization means there is a significantly lower risk of neural tube defects and other birth defects. If a woman is even thinking about getting pregnant or that is a possibility, having general good health habits is important for both her and her future child. Cut out excessive drinking and of course and drug usage and smoking. Eat a balanced diet and make sure you exercise a few times a week. And make an appointment with your OBGYN and/or primary care doctor, just to make sure everything is good. Be aware of any medications you are taking that may not be safe during pregnancy. And of course, it’s always a good idea to take care of yourself, whether or not you want to get pregnant.”

For more tips on how to get pregnant, read our Beginner’s Guide to Getting Knocked Up.

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