Electronic Frontier Foundation (EFF), a digital rights group, says that women who use period tracking apps should be aware of how their data is used.
This comes after the US reported decision to reverse the 1973 Roe v Wade legal order - which would render abortion illegal in 22 US states.
It is possible that the menstrual tracker apps could be used as a punishment for those who want to terminate their pregnancy.
Some apps may share data with third-parties.
It is not clear what apps do with period data, but third parties can feed this information back to big tech companies such as Amazon, Meta, and Google.
Cooper Quintin is a senior staff technologist at EFF. He told the BBC that period tracking apps developers should think about how much data they store about customers and the potential misuse of that data to cause harm or be used as a surveillance tool.
"Anyone who works with user data, particularly in the reproductive space, should think about how they can reduce the amount and length of data they keep and collect."
Period trackers are very popular among women who want to get pregnant. They can predict when ovulation will occur. It can also be used to track menopause. The "femtech market" is expected to exceed PS40bn by 2025.
Flo is the most widely used period tracker available. It has over 100 million users. It requires women to provide intimate information, such as their bleeding rate, unprotected sex and libido.
If privacy is a concern, women should read the small print. It states that the women's app will not share information about your "cycles, pregnancy or symptoms notes" and won't give out any personal details.
From 2016 to 2019, however, the company was found guilty of passing certain user health information to large tech companies. Flo claimed it was only for analytical purposes, but some women were furious.
With the possibility of the Roe v Wade ruling being reversed, many women who are considering illegal abortions in the US might be wondering if their menstrual data could be used by law enforcement against them.
Protocol, a tech outlet, reported that companies are able to resist subpoenas but hand over data about 80% of time.
Natural Cycles, a Swedish "digital contraceptive app", told BBC that this topic is very hot and offered some comfort to their users.
Natural Cycles, unlike other period tracking apps is FDA-cleared [US Food and Drug Administration] birthcontrol app. It is a medical device that adheres to very strict data privacy standards.
"All data on the app are safe and will remain protected. Natural Cycles has protected the data of each user since inception and will continue to do so.
Rhian Lewis, who manages the Online Abortion Resource Squad support group on Reddit, said that the BBC has noticed a spike in traffic to the group’s r/Abortion pages since the leak of an alleged US Supreme Court decision.
She stated that r/Abortion typically receives more than 500,000 pageviews per month from between 20 and 30,000 unique visitors. From Monday to Tuesday, our daily unique visitor count more than doubled."
These women aren't asking for privacy concerns, but they are asking how to get to a clinic, what resources they require, and legal information.
Ms Lewis said that for digital privacy concerns around abortion, she would refer people to the Digital Defense Fund as they are experts in this area.
The issue with this data is threefold. Who can discover that you have had an abortion in your life? What corporations could have access to your history of menstruation and what would they do? Is there a legal problem if law enforcement has this information? Ms Lewis said.
"We cannot make decisions for people. We know that people use digital tools in order to take care of themselves and to understand their bodies. This is especially true when they are trying to avoid getting pregnant.
"But data can be shared in multiple ways. It's important that everyone is informed and aware of all the implications, even those that may seem insignificant or farfetched at first.