Implantation bleeding and due date?


I went off the pill in July and waited until Dec to start trying for pregnancy. I had sex on Dec 18th and on Dec 31st I got a very light bleed (1-2 days). I had sex again in Jan. (10 and 12 days from my bleed in Dec) since I was trying. I got a positive result for a pregnancy test at the end of Jan. I’m trying to figure out how to tell if December’s bleed was an implantation bleed or a normal period. Would the implantation in the lining of the uterus throw off an ultrasound at 6 weeks to push my due date back 3-4 weeks?


Last Updated: July 22, 2013
Congratulations on your pregnancy! Also on the wisdom of waiting the several months to achieve a pregnancy after taking birth control pills. The most common and the most often used method of dating pregnancy is the gestational age, which is measured from the first day of the last menstrual period. In this way pregnancy is 40 weeks in duration instead of of the actual 38 weeks.

The other way of measuring the date is the fetal age measured from the estimated time of conception. Measuring this way it will be 38 weeks.

The third, and now becoming the standard of practice, is early ultra sound done in the first trimester of pregnancy. This dating is done by measurement of the crown-rump length of the fetus. This is thought to be accurate within plus or minus 3 days. In your case this may not have been done and your pregnancy is measured from the Dec. 31 bleed, which may have been an implantation bleed. Implantation bleeding or mucus usually occurs seven to nine days after conception. Unless measurement is done the ultrasound dates from the last menstrual period. You could ask to have this measurement done by your MD.

After the birth of your baby we encourage all mothers to breastfeed and use a natural method of fertility awareness which is better for mother and baby.

Good luck to you.

Theresa Mitchell

Answered By:

Theresa Mitchell, RN
Theresa Mitchell, RN, taught the Creighton Model FertilityCare System in the Oakland region.

Read more related questions

Is Progesterone Supplementation Moral?

I am currently 28 weeks pregnant with my second child. My first was born premature. My ob suggested progesterone injections starting at 16 weeks through…

Stressed I Might Be Pregnant

I am really stressed. I just got out of a four year relationship and I am worried I might become pregnant. No symptoms but it…

Are Fibroids Causing Bleeding During Pregnancy?

Hello, I am 45 years old and have large fibroids. I was about to have surgery to remove the womb. I am now seven weeks…

Should I Stop Nursing Since Pregnant

I am four weeks pregnant with my third pregnancy and still nursing my nine month old pretty frequently. I am 30. I nursed during my…

Progesterone in Pregnancy—History of Miscarriage and Pre-Term Delivery

We are seven weeks pregnant after trying for over a year. We miscarried last year after being on Prometrium for low progesterone and infertilty (infertile…

Scared I Am Miscarrying

I am writing because I am 13 weeks pregnant by ultrasound and LMP (but 11 weeks by my chart). This is my 4th pregnancy, I…

Scared Progesterone Can Harm My Baby

I am 32 years old and this is my first pregnancy. I have never had a miscarriage but when I started bleeding (hematoma) at 12…

Desperate for Explanation of Brown Spotting

I had sexual intercourse with my boyfriend and I am currently age 22. I finished my period on March 10th and the last time I…

Is My Progesterone Too Low for 15 Weeks Pregnant?

I am 42 years old and 16 weeks pregnant. I have had four first trimester losses (before nine weeks). I am MTHFR compound hetero (C677…

Did I Conceive May 11th or May 12th?

I was reading thru questions asking about “Who is the father?” One of the questions asked seemed very similiar to the situation that I’m going…

Did Progesterone Contribute to Baby’s Brain Cyst?

Hi, I was wondering about your knowledge on choroid plexus cysts. There were three found on my baby’s brain at my 19 week sonogram. I…

Estimating Date of Conception

How can my fertility doctor be sure I conceived on May 14? My period started on April 30. My six week five day ultrasound showed…

Create An Account

This is not a membership, this is an account for our CANFP website. If you decide you would like to sign up for one of our memberships later, you can do so with or without this account.

First Name *
Last Name *
E-mail *
Username *
Password *
Confirm Password *
Edit Profile
Order History
Shipping and Billing
Login Information
Notification Settings
Notification Subscriptions

CANFP conducts varied outreach programs to the community at large, in addition to serving our members (NFP users, teachers, and advocates).

CANFP provides education programs tailored to the audience, not only on Natural Family Planning, but on the wide variety of topics related to it.

Programs can be continuing education for NFP Professionals, introductory information for a lay audience of youth or adults new to the topic, or specifically tailored to the interests of a professional audience, such as educators, physicians, or clergy. Content is faith based or secular, whichever is suitable for situation.

CANFP offers a variety of resources for those just discovering Natural Family Planning, as well as to meet the varied needs of our CANFP Members. Most resources are available to any visitors to our site. Some resources do ask you to register as a site user in order to access them, others are available only to CANFP Members.

CANFP statewide conferences, regional events offered in collaboration with local partners, events featuring CANFP speakers, or exhbit, as well as other events throughout the state of interest to our NFP community.  Come meet one of our experts at one of these events or book a speaker for your own upcoming event.

CANFP depends on the gifts, talents, and generosity of our members and supporters. The success of our mission depends on the collaboration of our members. Please consider contributing your time treasure and talent through CANFP to share the good news of NFP with the world! Both volunteer and contracted positions available.

Stay informed by joining our email list

* indicates required
Which role(s) best describes you?