Conception Timing: Your Questions Answered

Time of conception

Hello, doctor.
I would like to ask some questions related to conception timing.
My last menstrual period started on September 9 and ended on September 14, with an average cycle length of six days.
However, my cycle is irregular; for instance, it was consistently 34 days from May to July this year, but I completely missed my period in August and went straight to September 9, resulting in a 42-day cycle.
I had intercourse with someone who is not my boyfriend on September 18 (with a condom) and then had unprotected intercourse with my boyfriend on September 27, during which he ejaculated inside me.
On October 8, I experienced abdominal discomfort and noticed a small amount of brown discharge.
I took a pregnancy test on October 12, which showed a faint second line.
That same day, I went to the hospital for an ultrasound, but they said the gestational age was too small to see the gestational sac.
On October 20, during a follow-up visit, they were able to see the gestational sac, and the doctor estimated it to be about four and a half weeks.
When I returned on November 2, the hospital measured the embryo size and found it to be six weeks and two days.
However, the timing does not match up with when I had intercourse with my boyfriend.
Is it possible that the child is not my boyfriend's? Is it possible to conceive four days after my period? Should I consider visiting different obstetricians? Is there a way to do prenatal DNA testing, and what would the cost be?

Niming, 20~29 year old female. Ask Date: 2020/11/15

Dr. Cao Guotao reply Obstetrics and Gynecology

Hello, it is possible that conception occurred on September 27, but there is developmental delay, which generally makes prenatal DNA testing unfeasible.
Wishing you good health.

Reply Date: 2020/11/15

More Info

Understanding conception timing can be quite complex, especially when dealing with irregular menstrual cycles and multiple sexual encounters. Let's break down your situation step by step to clarify your concerns.

First, it's important to understand the timing of ovulation and how it relates to conception. In a typical 28-day menstrual cycle, ovulation usually occurs around 14 days after the first day of your last menstrual period (LMP). However, since you mentioned that your cycles can vary significantly, this makes pinpointing ovulation more challenging. Given your last menstrual period started on September 9 and ended on September 14, if we assume a cycle length of around 34 days (as you mentioned was typical for you earlier in the year), ovulation could have occurred around September 23.
Now, regarding your sexual encounters: you had intercourse on September 18 with a condom and then again on September 27 without protection. The timing of these encounters is crucial. If you ovulated around September 23, the unprotected intercourse on September 27 would be within the fertile window, which typically spans a few days before and after ovulation. This means that it is indeed possible for you to conceive from the encounter with your boyfriend on September 27.

The light bleeding you experienced on October 8 could be implantation bleeding, which occurs when a fertilized egg attaches to the lining of the uterus. The fact that you received a faint positive pregnancy test on October 12 and then saw a gestational sac on ultrasound on October 20 aligns with the timeline of conception occurring around late September.

Now, regarding your concern about the paternity of the child: it is indeed possible for the child to be your boyfriend's if conception occurred after your encounter with him, especially since sperm can survive in the female reproductive tract for several days. However, if you are still uncertain, you may consider a paternity test.
Paternity tests can be conducted during pregnancy through a procedure called Non-Invasive Prenatal Paternity Testing (NIPP). This test analyzes fetal DNA found in the mother's blood and can be done as early as the 10th week of pregnancy. The cost of such tests can vary widely, typically ranging from $1,000 to $2,000, depending on the provider and the specific tests performed.

If you are feeling anxious about your situation, it may be beneficial to consult with a healthcare provider or a specialist in obstetrics and gynecology. They can provide you with more personalized advice and support, as well as help you navigate your options regarding paternity testing and any other concerns you may have.

In summary, based on your timeline, it is possible for your boyfriend to be the father of the child. However, if you have lingering doubts, a paternity test can provide clarity. It's essential to communicate openly with your healthcare provider about your concerns and explore your options moving forward.

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