The company is a leading provider of clinical trial solutions focused on providing solutions designed to significantly improve the quality and efficiency of clinical research, stimulate growth and promote compliance. The company's transformational solutions enable biopharmaceutical companies, contract research institutions ("CROs") and institutions to accelerate the provision of new treatments and treatments to patients while maintaining the highest standards of human protection. We leverage our differentiated strategic position at the center of the clinical trial ecosystem to provide new technological solutions for all relevant stakeholders to address key pain points throughout the clinical trial.
Since its inception, the company's end-to-end solutions have benefited more than 5000 biopharmaceutical and mid-range biopharmaceutical companies, 10, 000 research sites and millions of patients. The company's management estimates that in the past two years to December 31, 2020, WCG supported approximately 90% of all clinical trials worldwide, covering a wide range of treatment areas and trial phases, and during the same period, the company's solutions were utilized by 87% of all new drugs and therapeutic biological agents approved by the U.S. Food and Drug Administration (FDA). With more than 4000 employees worldwide, the company is at the heart of the company's mission and platform, with operations in 71 countries. From March 2020 to February 2021, we supported more than 4000 global clinical trials, which attests to our important expertise.
Growth over the years
From 2018 to 2020, the company's revenue grew by about 16 per cent a year, from $345.6 million to $463.4 million, and the adjusted EBITDA margin (defined as adjusted EBITDA divided by revenue) reached 47 per cent in 2020. Our revenues grew by about 33 per cent in the three months to March 31, 2021, from $103.5 million to $137.6 million, while adjusted EBITDA margins reached 43 per cent in the three months to March 31, 2020.
In 2019 and 2020, 74% and 69% of the company's revenue growth was organic revenue growth, respectively. A net loss of $2.6 million in 2018, a net profit of $18.2 million in 2019 and a net loss of $95.3 million in 2020, mainly affected by transactions. In addition, our net losses for the three months ended March 31, 2021 and 2020 were $20.6 million and $30.1 million, respectively. The company's adjusted EBITDA grew by about 50%, from about $146 million in 2018 to about $218.4 million in 2020. Adjusted earnings before interest and tax (EBITDA) increased by about 24% in the three months ended March 31, 2021, from $47.6 million to $59.1 million, and to three months in the three months ended March 31, 2020. From 2019 to 2020, the company's bookings increased by about 12%, from $555.2 million to $621.8 million. In the three months ended March 31, 2021, the company's bookings increased by about 55%, from $171.8 million to $266.2 million, and in the three months to March 31, 2020. As of March 31, 2021, the company's top 25 customers purchased an average of more than 4 solutions, each with revenue of more than $2 million. The company estimates that the current opportunity will exceed $1.6 billion by further cross-selling existing solutions to these customers. WCG has a track record of acquiring and integrating leading technologies and solutions into our platform, with 31 acquisitions completed since 2012.
Performance guidance
For the three months ended June 30, 2021, the company expects bookings to be between $237.7 million and $248.8 million, compared with $149.5 million for the three months ended June 30, 2020. The overall expected increase in bookings is mainly due to the quarter-on-quarter increase in the number of studies submitted, as well as the increase in customer pipeline learning after COVID, the addition of Trifecta training to our solution products and the victory of new customers.
Revenue for the three months ended June 30, 2021 is expected to be between $143.5 million and $150.2 million, compared with $108.8 million for the three months ended June 30, 2020. The increase in overall expected revenue was mainly due to strong demand for the company's patient participation products, increased demand for ethics review services, and the acquisition of Trifecta, Avoca and internal products.
We expect a net loss of between $27.1 million and $23.3 million for the three months ended June 30, 2021, compared with a net loss of $23.8 million for the three months ended June 30, 2020. The change in expected net loss is mainly due to higher income offset by higher income, including equity compensation, to support revenue growth, higher taxes and IPO-related expenses.
For the three months ended June 30, 2021, the company expects adjusted EBIT to be between $64.1 million and $68.4 million, while adjusted EBIT for the three months ended June 30, 2020 is between $54.1 million. The expected change in adjusted EBITDA is mainly due to increased revenue and growth, proportional increases in related operating expenses, as well as increases in acquisition-related contingencies, consolidation-related expenses, IPO-related expenses and equity-based compensation.
Market space
As part of the clinical trial market, the specific market segments covered by WCG (including IRB, research planning and site optimization, patient participation, and scientific and regulatory reviews) account for approximately $9 billion in 2021 and we expect annual growth of 14% between 2021 and 2023.
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