increase in both Adjusted EBITDA and Adjusted EBITDA margin reflect the operating efficiencies realized on our higher revenues. Adjusted EBITDA margin on incremental revenue in 2021 was 22.4%.
Please refer to Annex A for a reconciliation of gross margin excluding the impact of stock-based compensation expense to gross margin and Adjusted EBITDA to net income, as well as the calculation of Adjusted EBITDA margin on incremental revenue.
Cash Flow
Net cash provided by operating activities in 2021 was $26.0 million, compared to net cash provided by operating activities of $36.2 million in 2020. The decrease was primarily due to the previously disclosed revisions in the arrangements with pharmacy partners, which changed the timing of the payments we receive, and other timing items in each period. Net cash provided by operating activities for the fourth quarter of 2021 was $8.8 million, compared to net cash provided by operating activities of $6.5 million in the prior year period. The improvement was due primarily to the higher profitability, as well as the timing of billing and collections on quarterly cash flows.
Balance Sheet and Financial Position
As of December 31, 2021, the company had total working capital of approximately $159.7 million and no debt. This included cash and cash equivalents and marketable securities of $119.4 million, reflecting an increase of $5.1 million from the balances as of September 30, 2021.
Key Metrics
The company had 191 clients as of December 31, 2021, as compared to 135 clients as of December 31, 2020.
| | Three Months Ended December 31, | | Year Ended December 31, | |
| | 2021 | | 2020 | | 2021 | | 2020 | |
ART Cycles* | | 7,623 | | 5,719 | | 28,413 | | 19,003 | |
Utilization – All Members** | | 0.52 | % | 0.50 | % | 1.30 | % | 1.16 | % |
Utilization – Female Only** | | 0.46 | % | 0.45 | % | 1.07 | % | 0.97 | % |
Average Members | | 2,899,000 | | 2,305,000 | | 2,812,000 | | 2,191,000 | |
* Represents the number of ART cycles performed, including IVF with a fresh embryo transfer, IVF freeze all cycles/embryo banking, frozen embryo transfers, and egg freezing.
** Represents the member utilization rate for all services, including, but not limited to, ART cycles, initial consultations, IUIs, and genetic testing. The utilization rate for all members includes all unique members (female and male) who utilize the benefit during that period, while the utilization rate for female only includes only unique females who utilize the benefit during that period. For purposes of calculating utilization rates in any given period, the results reflect the number of unique members utilizing the benefit for that period. Individual periods cannot be combined as member treatments may span multiple periods.
Financial Outlook
“Coming off of a record sales season, we are excited for the year ahead, after successfully launching with the largest number of new clients and new covered lives in our history,” said Mr. Anevski. “We believe that Progyny is in its best-ever competitive position, and all of the macro trends that have been fueling our rapid growth remain intact. Our focus has always been to continue to build and enhance our business so that we are capable of achieving sustained, long-term success. We are achieving this through the platform that we have built, which has enabled us to continue our high rate of client retention as well as accelerate our new client additions each year. We are cautiously optimistic that the pandemic may be coming to an end, and the world hopefully will be returning to a more normal state. At this point, every indicator we monitor supports that we will have another successful selling season, driven by our superior solution, our delivery of the highest levels of service, and our industry-leading clinical outcomes.
We are pleased to announce our guidance for the first quarter and the full year 2022, which reflects both significant ongoing topline growth of 50% at the midpoint of the range for 2022, as well as the continued expansion of our margins.”
| o | Revenue is expected to be $730.0 million to $775.0 million, reflecting growth of 46% to 55% |