Is My Sister's Baby Her Boyfriend's? Pregnancy Paternity

Is the pregnancy from my boyfriend?

Hello, doctor.
I would like to ask about my sister, who is currently pregnant.
She has a boyfriend, but after drinking, she had sexual intercourse with another man between April 16 and April 30.
She doesn't remember the exact date, but her period came on May 9 and lasted for 3 to 5 days.
She mentioned that her menstrual cycle is irregular.
When she took a pregnancy test in mid-June, it confirmed that she was pregnant, with a due date of February 16 next year.
She is very anxious about whether the child is her boyfriend's or the other man's, as her calculations do not match those of the hospital.
She is struggling to face her boyfriend and is afraid to ask the doctor who is monitoring her pregnancy.
That’s why she is inquiring here.

Ms. Li, 20~29 year old female. Ask Date: 2018/11/11

Dr. Huang Jianzhong reply Obstetrics and Gynecology

After drinking, she had sexual intercourse with a man (referred to as A) between April 16 and April 30.
She doesn't remember the exact date, but her menstrual period started on May 9 and lasted for 3 to 5 days.
She mentioned that her menstrual cycle is irregular.
When she took a pregnancy test in mid-June, she found out she was pregnant, with a due date of February 16 of next year.
She feels very anxious about whether the child is her boyfriend's or A's.
If the child is A's, her menstrual period on May 9 would not have occurred.

Reply Date: 2018/11/11

More Info

To determine the paternity of your sister's baby, we need to analyze the timeline of events and the biological factors involved in conception. Based on the information provided, your sister had sexual relations with two different men around the time of her ovulation, which complicates the determination of the baby's father.

1. Understanding the Menstrual Cycle and Ovulation: Your sister's menstrual cycle is crucial in understanding when she might have ovulated. If her cycle is irregular, it can be challenging to pinpoint the exact day of ovulation. Typically, ovulation occurs about 14 days before the start of the next menstrual period. If her last period started on May 9 and lasted for 3-5 days, she likely ovulated around May 23 to May 25, assuming a typical cycle length.

2. Timing of Sexual Encounters: Your sister had sexual relations with "A" between April 16 and April 30, and then with her boyfriend after that. If she had her period on May 9, it is unlikely that the encounter with "A" would lead to pregnancy unless she had a very irregular cycle that allowed for late ovulation. The key factor here is whether she ovulated after her period ended or if she had a late ovulation.

3. Pregnancy Testing and Confirmation: If she tested positive for pregnancy in June, it would be essential to consider the timing of her ovulation. If she ovulated around May 23-25, and had unprotected intercourse with her boyfriend shortly after that, it is possible that the baby could be her boyfriend's. However, if she ovulated later than expected, there could be a chance that "A" is the father.

4. Ultrasound Dating: The most reliable way to determine the gestational age of the fetus is through an ultrasound. An ultrasound can provide a more accurate estimate of the due date based on the size of the fetus. If the ultrasound suggests a gestational age that aligns more closely with the dates of intercourse with her boyfriend, this would support the idea that he is the father.

5. Genetic Testing: If there is still uncertainty about paternity, the most definitive way to confirm the biological father of the child is through genetic testing after the baby is born. A paternity test can provide clear answers and help alleviate any doubts.

6. Emotional and Ethical Considerations: It is understandable that your sister is feeling anxious about the situation. Open communication with her boyfriend is crucial, as honesty can help build trust in their relationship. It may also be beneficial for her to seek counseling or support to navigate her feelings and the potential outcomes of the situation.

In conclusion, while the timeline suggests that the baby could likely be her boyfriend's, the irregularity of her menstrual cycle and the timing of her ovulation make it difficult to be certain without further medical evaluation. Encouraging her to discuss her concerns with a healthcare provider and consider genetic testing after the baby is born may provide the clarity she needs.

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