Shauna Stewart Douglas was struggling with infertility. It caught her and husband, John, by surprise.

“I assumed that if you can get pregnant once, then you can get pregnant again,” Douglas told Fox News.

She had become pregnant almost two years earlier with her daughter, but this time around even in vitro fertilization (IVF) wasn’t working. At age 35, Douglas found herself struggling with secondary infertility.

“People always say to imagine what you want your kitchen table to look like in the future when you’re thinking about how many kids to have," Douglas said. "And in my mind it has been my husband and all of our kids and that was all fading away. It was all going away."

Reports estimate that over 3 million couples in the United States face secondary infertility, which according to the Mayo Clinic is the inability to become pregnant or to carry a baby to term after previously giving birth.

Dr. Kecia Gaither, an OB-GYN and director of perinatal services at NYC Health + Hospitals/Lincoln, says several conditions can cause secondary infertility like obesity, polycystic ovary syndrome (PCOS), the use of some medications, prior surgery, endometriosis, issues with cervical mucus and the age of both partners.

“Many health conditions can be present without symptoms, until such a time as the couple wishes to become pregnant,” Gaither told Fox News. “If there is an issue within a year of trying in couples less than 35 years of age or after six months in couples older than 35, it’s time to see your physician.”

Douglas, founder of Permission to Profit, said they tried two rounds of IVF--with the second time ending in miscarriage--before they decided that they “couldn’t do it anymore.”

“Maybe it would have happened if we had kept on going and trying again and again, but I couldn't do it, I just I couldn't do the rollercoaster anymore.”

Douglas said a medical condition, which she preferred not to disclose, and her age of almost 36 when they started trying for their second child, most likely led to her secondary infertility.

“The biggest culprit typically in secondary infertility is the ovarian reserve,” Dr. Brooke Hodes Wertz, a reproductive endocrinologist at NYU Langone Fertility Center told Fox News. “The ovary loses eggs in number and quality over time. So it gets harder to get pregnant over time.”

Treatment for secondary infertility is the same as it is for primary infertility. Doctors should first start with an evaluation of both partners, Wertz said.

“You're going to do a semen analysis for the male partners," Wertz explained. "The females typically undergo blood testing that can look at how their ovaries are doing as well as testing to look at the inside of their cavity, whether it's a hysterosalpingogram or an ultrasound, to look at the cavity and make sure the tubes are open."

The most common blood tests for women are called FSH (follicle-stimulating hormone), which give a reflection of the egg quality and AMH (anti-mullerian hormone) which show the number of eggs the patient has.

NEW YORK DOCTOR OFFERS PATIENTS STRUGGLING WITH INFERTILITY A LOW-COST AND NEEDLE-FREE IVF TREATMENT

If there appears to be an issue, a doctor may recommend certain treatments at a fertility clinic.

“We have simple treatments which involve oral medicine and often taking the sperm and releasing it very close to where the egg gets released,” Wertz said. “And then we have more aggressive treatments like in vitro fertilization (IVF).”

IVF typically uses fertility drugs to induce ovulation and then extracts the eggs and fertilizes them with sperm in a lab. Once the embryo forms, doctors then transfer the embryo into the uterus.

A lot of women don't realize a couple of years makes a difference — Dr. Brooke Hodes Wertz, NYU Langone Fertility Center

Wertz also recommended egg freezing as a way to possibly avoid secondary infertility.

“We have the ability to freeze eggs and embryos when the ovaries are younger and put them back in at an older age when it would have been harder to get pregnant,” Wertz said. “A lot of women don't realize a couple of years makes a difference.”

While there have been success stories among women who have frozen their eggs when they are over 40 years old, Wertz said it is preferable to freeze your eggs earlier in life, ideally before the age of 35.

Even though Douglas, now 41, didn’t think that more rounds of IVF would give her family a second child and her daughter a sibling, there was another option for her--adoption.

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“Families are made up in all kinds of different ways and, for us, we have a biological child and we have an adoptive child,” Douglas said. “Going down that path was an incredibly beautiful thing because now we have my son, which is amazing and I'm really grateful for that.”