When Does Week 1 of Pregnancy Start? – Symptoms & Key Facts

By (embryologist) and (fertility counselor).
Last Update: 02/28/2018

As a general rule, the first week of pregnancy starts with the beginning of the last menstrual period (LMP). In fact, at this point, embryo implantation and pregnancy per se have not taken place yet.

Gynecologists consider the first day of the LMP as the beginning of pregnancy because determining the exact day in which fertilization takes place is quite complicated.

During this week, the woman still cannot have any pregnancy signs, since conception has not occurred yet. Symptoms such as stomach pain, headache, bloating, etc. are related to the premenstrual syndrome (PMS) and the normal pains during menses.

What happens in the first week?

Actually, during what we refer to as first week of pregnancy, the woman has not fallen pregnant yet. This week just marks the beginning of a new menstrual cycle—the one in which pregnancy is going to happen. So, throughout week 1, you just have your normal period, which usually lasts between 3 and 7 days.

From this week onwards, your body starts releasing gonadotrophic hormones FSH and LH again. As a consequence, your ovaries start developing new follicles and secreting sex hormones.

Thanks to the release of estrogens by the ovary, your endometrium (lining of the uterus) proliferates again and starts thickening right after your last menstrual period ends.

The endometrium is the inner lining of the uterus, which thickens with each new menstrual cycle and is shed during menstruation. To learn more, read: What's the Role of the Endometrium?

In women whose menstrual cycles are too short or irregular, ovulation may occur during this week. In other words, they can get pregnant while on their period if they engage into unprotected sexual activity.

Pregnancy symptoms at week 1

The symptoms that you are likely to notice at week 1 are the ones typically associated with the menstrual period. The following are the most usual discomforts:

  • Bleeding
  • Abdominal pain
  • Side pain
  • Ovarian pain
  • Sore breasts
  • Cramps
  • Headache, fainting and/or dizziness
  • Gastrointestinal symptoms: nausea, vomiting, stomach pain, gas, diarrhea, constipation, etc.
  • Water retention and bloating
  • Hormonal acne and/or breakout of pimples
  • Mood swings

Broadly speaking, the very early signs of pregnancy at first week are actually the common menstrual discomforts. These symptoms may be noticed before your menses, a phase that is known as Premenstrual Syndrome or PMS and is commonplace during the week(s) prior to a woman's menstruation.

Dos and don'ts

If you have fallen pregnant unintentionally, it is likely that you have not changed your habits during the weeks prior to taking the pregnancy test and finding out that you are pregnant.

But if you were trying to get pregnant, whether naturally or through a fertility treatment, you should start taking care of yourself and preparing your body for a future pregnancy. The following are some basic tips:

Healthy foods & diet

There is no special diet to follow or specific foods to eat at week one of pregnancy. However, it is recommended that you acquire healthy habits, including nutritious foods from all food groups, always eating five meals a day.

Including protein-rich foods like meat, fish, and eggs is crucial. Eating fruits, vegetables, and cereals on a daily basis is highly recommended as well.

When pregnant, all women need an extra dose of calcium and folic acid. For this reason, if you are trying to conceive, you should include dairy products in your diet, as well as folic acid supplementation.

There are certain foods that you should avoid or limit, including coffee and tea. Caffeine inhibits iron absorption, an essential nutrient to prevent anemia in pregnant women.

Finally, you should take a series of precautions to prevent the risk of toxoplasmosis and listeria, two serious diseases for pregnant women. Avoiding unwashed foods and vegetables, as well as raw or undercooked meats, fish, or seafood (e.g. ham or sushi).

Things not to do

Giving up smoking and drinking not only during pregnancy, but also in the time before conception is key to a healthy, ongoing pregnancy. Pre-conception cigarette smoke and alcohol drinking can affect fetal development and increase the risk of miscarriage or preterm birth.

Nicotine hinders the transfer of oxygen to the fetus through the placenta and can cause respiratory diseases in newborns.

Also, alcoholic drinks can cause physical and mental birth defects. Alcohol use in pregnancy increases the chances for your baby to develop Fetal Alcohol Syndrome (FAS), which effects include malformations of the skeletal system.

Preconception planning

Are you trying to get pregnant? If so, you should consider getting yourself checked and well informed as soon as possible. In the era of technology, you have plenty of resources for you to get trustworthy information about pregnancy.

Visit your doctor, attend support groups or even talk to women who have been pregnant recently. They are all great opportunities for you to get answers regarding what to eat, dos and don'ts, exercising, fetal development, etc.

FAQs from users

Can you get pregnancy symptoms at 1 week?

By Zaira Salvador B.Sc., M.Sc. (embryologist).

Actually, the first week of pregnancy coincides with the last menstrual period before the woman gets pregnant. So, actually, the symptoms that the woman has during this week are the typical discomforts of the menstrual period: stomach pain, cramps, headaches, nausea...

On the other hand, getting pregnancy symptoms as early as 1 week after conception is also highly unlikely. To sum up, you may start having pregnancy symptoms as early as a few days before you miss your period.

Can you test for pregnancy at 1 week?

By Zaira Salvador B.Sc., M.Sc. (embryologist).

No, a pregnancy wouldn't work at 1 week. If you do so, you may get a negative result. Given that conception has not occurred at this point, the hCG hormone is still not present in your body, which is the hormone detected by pregnancy tests.

Learn more: When to Do a Pregnancy Test? – Instructions for Use, Results & Accuracy.

Can ultrasound detect pregnancy at 1 week?

By Zaira Salvador B.Sc., M.Sc. (embryologist).

No, it is not possible yet. A gestational sac can be seen as early as the 5th week of pregnancy, or 3 weeks after conception. If no sac is seen by this time, it is possible that the woman ovulated late.

What does pregnancy feel like at 1 week?

By Zaira Salvador B.Sc., M.Sc. (embryologist).

During the first week, you are still having your monthly menses, so you will feel the common symptoms of menstruation. You may start getting pregnancy symptoms after embryo implantation. From this moment on, your body produces hCG, the hormone responsible for the most common symptoms of pregnancy.

Recommended for you: What Are the Earliest Symptoms of Pregnancy Before Missed Period?

Is it normal to pee a lot in the first week of pregnancy?

By Zaira Salvador B.Sc., M.Sc. (embryologist).

Frequent urination is one of the earliest signs of pregnancy, but it's a consequence of the presence of the hCG hormone in your body. Since hCG is still not present in the body at week 1, it's unlikely that this symptom is caused by pregnancy.

Can 1 week pregnancy be aborted?

By Zaira Salvador B.Sc., M.Sc. (embryologist).

No, it is not possible, because embryo implantation and the subsequent pregnancy has not taken place yet. For this reason, taking abortion pills such as Cytotect, which is composed of Misoprostol, is not recommended until a pregnancy is confirmed with a positive pregnancy test.

If you think you may be pregnant, it is possible for you to use the morning-after pill or emergency pill in order to avoid an unplanned pregnancy. This birth control method inhibits ovulation and alters the endometrium so that embryo implantation is not possible.

Suggested for you

Are you looking for the very early signs and symptoms of pregnancy? Then you should know that they start being noticed as early as on the third week of pregnancy. Find them out here: 3 Weeks Pregnant – Symptoms & Size of the Fetus.

To get an overall idea of the changes women go through in the first month of pregnancy, read: What Happens in the First Month of Pregnancy? – Symptoms & Tips.

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 Zaira Salvador
Zaira Salvador
B.Sc., M.Sc.
Bachelor's Degree in Biotechnology from the Technical University of Valencia (UPV). Biotechnology Degree from the National University of Ireland en Galway (NUIG) and embryologist specializing in Assisted Reproduction, with a Master's Degree in Biotechnology of Human Reproduction from the University of Valencia (UV) and the Valencian Infertility Institute (IVI) More information about Zaira Salvador
License: 3185-CV
Adapted into english by:
 Sandra Fernández
Sandra Fernández
B.A., M.A.
Fertility Counselor
Bachelor of Arts in Translation and Interpreting (English, Spanish, Catalan, German) from the University of Valencia (UV) and Heriot-Watt University, Riccarton Campus (Edinburgh, UK). Postgraduate Course in Legal Translation from the University of Valencia. Specialist in Medical Translation, with several years of experience in the field of Assisted Reproduction. More information about Sandra Fernández

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