Finding an investment that could go parabolic within a few years of purchasing it is a hard-enough feat. Making matters even more complicated, the real battle may be hanging on to a booming stock for the long haul and not selling too early.

All too frequently, investors receive a quick 50% or even 100% return from a stock and happily cast it aside in the name of "making a quick profit." Though these short-term profits are authentic, investors must remember that they might be throwing away a business in the early chapters of a tremendous growth story.

However, Progyny (PGNY) and Doximity (DOCS -1.46%) are companies I am confident I won't be tempted to sell should they go parabolic soon. Home to market-leading positions in their respective niches of the healthcare market, these transformative businesses operate at the heart of two robust megatrends, making them super stocks to buy and hold for the long haul.

Progyny: Helping to address worrisome infertility rates

With the World Health Organization finding that infertility affects one in six people today -- a mark that rose from one in eight four years ago -- Progyny's fertility solutions may make it one of the easiest stocks to root for out there. Providing its network of fertility experts through its specialized platform, Progyny serves 384 corporate clients and over 5.3 million members, figures which grew by 41% and 25% in its most recent quarter. 

Fueled by this incredible customer-count growth, the company saw revenue spike by 43% over the last year. And this growth is far from a one-off, with Progyny's sales rising nearly sixfold since its 2019 initial public offering (IPO). Despite this incredible run, the company's stock price has languished over the last two years after quadrupling right out of the gates.

This rapidly growing revenue growth, paired with Progyny's struggling share price, has left it trading at all-time lows on a price-to-sales (P/S) basis.

PGNY PS Ratio Chart

PGNY PS Ratio data by YCharts.

As Progyny operates in what is quickly proving to be a fiercely competitive niche of the healthcare industry, the market seems to be taking a more cautious outlook on its potential. However, the company has delivered fertility data superior to national averages in the United States for seven consecutive years.

Reporting a pregnancy rate 17% higher, miscarriage rate 25% lower, and live birth rate 27% higher than national averages, Progyny's exclusive focus on the fertility niche is providing best-in-class results for members and clients alike. Thanks to these incredible results -- which are audited by a third party -- the company saves its business clients an estimated 25% to 30% over traditional benefits programs.

Counting less than 5% of businesses with more than 8,000 employees as clients, Progyny's marathon-like growth opportunity could still be in its early miles. Trading at an all-time low P/S sales ratio while being consistently profitable and free-cash-flow-positive, Progyny looks like a super stock that not only could go parabolic in the next few years but be worth holding for decades beyond.

Doximity: A dominant healthcare network of a different kind

Considering itself to be the "Bloomberg for physicians," Doximity's cloud platform is used by a staggering 80% of doctors in the U.S. Its power users often utilize the platform to send digital faxes and e-sign documents, set schedules for their employees, and make telehealth visits. Meanwhile, less frequent users are still incentivized to use the app to scroll through relevant medical news, network with peers, or search for new career opportunities or employees.

Thanks to this litany of use cases for physicians, the platform is quickly becoming a lucrative target for pharmaceutical and hospital-system advertisers looking to get their products in front of doctors' eyes.

Counting all 20 of the top 20 largest pharmaceutical manufacturers and hospital and health systems as customers, Doximity hopes to eliminate those annoying pharma ads that viewers see during time-outs in their favorite teams' sports games. Instead of relying upon reaching out to consumers (who would potentially ask their doctor about the drugs in what feels like a wildly backward manner), Doximity's marketing solutions go straight to the physicians themselves.

Despite all 20 of the top pharmas and hospitals being customers, the company only has a 5% penetration rate among the 430 prescription brands in the U.S. that generate more than $100 million in annual sales, leaving a vast growth runway.

Best yet for investors, Doximity generates a ridiculous free-cash-flow (FCF) margin of 43% -- or 31% if we remove stock-based compensation. However, with revenue growth slowing dramatically in 2023 as advertising spending has declined, Doximity's share price has plummeted.

With the stock now trading at 26 times FCF (or 33 without stock-based compensation), the company's massive potential in the healthcare-advertising industry looks reasonably priced at just 15% above its all-time low valuation.

DOCS Price to Free Cash Flow Chart

DOCS Price to Free Cash Flow data by YCharts.

While short-term weakness in the ad industry could weigh on Doximity's short-term potential, its stock price could go parabolic as the macroeconomic environment improves and its valuation rises from near all-time lows. Powered by the largest physician network of its kind -- and an incredibly valuable one at that, it seems -- Doximity is perfectly positioned to grow its relationships with its massive pharmaceutical and health customers for decades to come.